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link管理  ›  JavaScript SyntaxError - Unexpected number - GeeksforGeeks
https://www.geeksforgeeks.org/javascript-syntaxerror-unexpected-number/
胆小的青椒
7 月前
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        • The Unexpected number error in JavaScript occurs when the JavaScript engine encounters a number in a place where it isn’t syntactically valid. This error is categorized as a SyntaxError, indicating that there’s a problem with the structure of your code.

          Message 

          SyntaxError: Unexpected number

          Error Type 

          SyntaxError

          Cause of the Error

          The “Unexpected number” error arises when a numeral is improperly positioned or used within your JavaScript code. This can happen due to:

          • Misplaced Numbers: Numbers appearing in contexts where they are not allowed.
          • Malformed Expressions: Errors in the way expressions are written, often due to missing operators or incorrect concatenation.
          • String Concatenation Issues: Including numbers in strings without proper concatenation.

          Correct Usage

          To avoid this error, ensure that numbers are used correctly in expressions, variables, and other structures. Properly format expressions and strings to align with JavaScript’s syntax rules.

          Example 1: Misplaced Number

          In this example, a number is placed directly after a variable without an operator or space, causing the error:

          JavaScript 
          let result = 10 20; // SyntaxError: Unexpected number

          Output:
          

          SyntaxError: Unexpected number
          Correction: Ensure that numbers are properly separated by operators or spaces.
          

          let result = 10 + 20; // Correct usage
          Example 2: Incorrect String Concatenation
          In the given below example a number is incorrectly included within a string without proper concatenation, causing the error. 
          
            JavaScript
    
          let message = "The result is: " 42;
console.log(message);

          Ouptut:
          

          SyntaxError: Unexpected number
          Correction: Use concatenation to properly include numbers in strings.
          

          let message = "The result is :" + 42; // Correct usage
          The SyntaxError: Unexpected number indicates a problem with the placement or use of numerals in your code. To resolve it, ensure that numbers are used in the correct context, and that all expressions and strings are properly formatted and concatenated.
          

          FAQs-JavaScript SyntaxError – Unexpected number
          What causes a SyntaxError: Unexpected number?
          This error is caused by improper placement or usage of numbers in your code, such as missing operators between numbers, incorrect string concatenation, or malformed expressions.
          

          How do I fix a SyntaxError: Unexpected number?
          Ensure numbers are correctly placed within expressions, variables, or strings. Check for missing operators and correct concatenation of strings with numbers.
          

          What is the difference between SyntaxError: Unexpected number and ReferenceError?
          SyntaxError: Unexpected number indicates a problem with the structure of the code, such as incorrect number placement. ReferenceError occurs when a variable or function is referenced before it is declared or initialized.
          

          Can SyntaxError: Unexpected number occur in JSON data?
          Yes, if JSON data contains a syntax error, such as a misplaced number or incorrect format, parsing the JSON with JSON.parse() will throw a SyntaxError.
          

          How does SyntaxError: Unexpected number affect debugging?
          This error indicates a syntax issue in your code that must be resolved for the code to run correctly. Debugging involves checking the correct placement of numbers and ensuring proper syntax in expressions and strings.
          
                
          JavaScript SyntaxError - Unexpected token
          
                
          This JavaScript exceptions unexpected token occur if a specific language construct was expected, but anything else is typed mistakenly. This could be a simple typing mistake. Message: SyntaxError: expected expression, got "x" SyntaxError: expected property name, got "x" SyntaxError: expected target, got "x" SyntaxError: expected rest argument name,
          
                
          JavaScript SyntaxError – Unexpected identifier
          
                
          An “Unexpected identifier” error occurs when you have put an identifier where it is not supposed to be in your JavaScript code, it results in a syntax error that makes the interpreter fail to read the code, mostly, it happens because of incorrect identification or location in relation to expressions, variables and other structures found within the
          
                
          JavaScript SyntaxError – Unexpected end of input
          
                
          A SyntaxError: Unexpected end of input error in JavaScript occurs when the interpreter reaches the end of script it is reading and it indicates that the code is incomplete, this error will prevent the code from running and mostly happens when a closing bracket, quote or parenthesis are missing, here's how to understand this error, its causes and ho
          
                
          JavaScript SyntaxError – Unexpected reserved word
          
                
          A "SyntaxError: Unexpected reserved word" error in JavaScript is when a reserved word is used incorrectly, generally in a different identifier kind of context, this error will not allow the code to run and frequently results from using keywords as variable names, function names or by putting them at suitable positions in the code, in this article w
          
                
          JavaScript SyntaxError – Unexpected template string
          
                
          A JavaScript error, “SyntaxError: Unexpected template string”, is raised when a template string ( ``) is misused or misplaced, although these strings permit the use of embedded expressions and multi-line strings, using them wrongly would cause the syntax to break, let’s get to know what this error is all about, its causes and how it can be correcte
          
                
          JavaScript SyntaxError - Unexpected string
          
                
          The occurrence of a “SyntaxError: Unexpected string” in JavaScript happens when a programmer uses string data type in an expression, statement, or declaration where it is not appropriate, this syntax error stops the script and it may happen due to incorrect placement of strings in expressions, variables, etc, let's get to know this error better thr
          
                
          JavaScript Error Handling: Unexpected Token
          
                
          Like other programming languages, JavaScript has define some proper programming rules. Not follow them throws an error.An unexpected token occurs if JavaScript code has a missing or extra character { like, ) + - var if-else var etc}. Unexpected token is similar to syntax error but more specific.Semicolon(;) in JavaScript plays a vital role while wr
          
                
          Unexpected token error for catch JavaScript
          
                
          In this article, we will try to understand the fact that why we receive Unexpected token errors while we are dealing with try/catch in JavaScript, and with the help of certain coding examples (in JavaScript itself) we will try to see how we may be able to resolve such token error properly. Unexpected token error is usually regarded as a subset erro
          
                
          JavaScript SyntaxError "variable" is a reserved identifier
          
                
          This JavaScript exception variable is a reserved identifier occurs if the reserved keywords are used as identifiers. Message: SyntaxError: The use of a future reserved word for an identifier is invalid (Edge) SyntaxError: "x" is a reserved identifier (Firefox) SyntaxError: Unexpected reserved word (Chrome) Error Type: SyntaxError What happened? Whe
          
                
          JavaScript SyntaxError - Missing ) after argument list
          
                
          This JavaScript exception missing ) after argument list occurs if there is an error in function calls. This could be a typing mistake, a missing operator, or an unescaped string. Message: SyntaxError: Expected ')' (Edge) SyntaxError: missing ) after argument list (Firefox) Error Type: SyntaxError Cause of Error: Somewhere in the code, there is an e
          
                
          JavaScript SyntaxError - Missing ; before statement
          
                
          This JavaScript exception missing ; before statement occurs if there is a semicolon (;) missing in the script. Message: SyntaxError: Expected ';' (Edge) SyntaxError: missing ; before statement (Firefox) Error Type: SyntaxError Cause of Error: Somewhere in the code, there is a missing semicolon (;). You need to provide it so that JavaScript can pars
          
                
          JavaScript SyntaxError - Missing = in const declaration
          
                
          This JavaScript exception missing = in const declaration occurs if a const is declared and value is not provided(like const ABC_DEF;). Need to provide the value in same statement (const ABC_DEF = '#ee0'). Message: SyntaxError: Const must be initialized (Edge) SyntaxError: missing = in const declaration (Firefox) SyntaxError: Missing initializer in
          
                
          JavaScript SyntaxError - Missing name after . operator
          
                
          This JavaScript exception missing name after . operator occurs if the dot operator (.) is used in the wrong manner for property access. Message: SyntaxError: missing name after . operator Error Type: SyntaxError Cause of Error: The dot operator (.) is used to access the property. Users will have to provide the name of the properties to access. Some
          
                
          JavaScript SyntaxError  - "use strict" not allowed in function with non-simple parameters
          
                
          This JavaScript exception 'use strict' not allowed in function occurs if strict modes 'use strict' statement is used at the beginning of a function with default parameters, rest parameters, or destructuring parameters. Message: Edge: Cannot apply strict mode on functions with non-simple parameter list Firefox: SyntaxError: "use strict" not allowed
          
                
          JavaScript SyntaxError - JSON.parse: bad parsing
          
                
          This JavaScript exception thrown by JSON.parse() occurs if string passed as a parameter to the method is invalid. Message: SyntaxError: JSON.parse: unterminated string literal SyntaxError: JSON.parse: bad control character in string literal SyntaxError: JSON.parse: bad character in string literal SyntaxError: JSON.parse: bad Unicode escape SyntaxEr
          
                
          JavaScript SyntaxError - A declaration in the head of a for-of loop can't have an initializer
          
                
          This JavaScript exception a declaration in the head of a for-of loop can't have an initializer occurs if the for -of loop contains an initialization expression like |for (var i = 0 of iterable)|. This is not valid initialization in for-of loops. Message: SyntaxError: for-of loop head declarations cannot have an initializer (Edge) SyntaxError: a dec
          
                
          JavaScript SyntaxError - Applying the 'delete' operator to an unqualified name is deprecated
          
                
          This JavaScript exception applying the 'delete' operator to an unqualified name is deprecated works in strict mode and it occurs if variables are tried to be deleted with the delete operator. Message: SyntaxError: Calling delete on expression not allowed in strict mode (Edge) SyntaxError: applying the 'delete' operator to an unqualified name is dep
          
                
          JavaScript SyntaxError - Function statement requires a name
          
                
          This JavaScript exception function statement requires a name that occurs if there is any function statement in the script which requires a name. Message: Syntax Error: Expected identifier (Edge) SyntaxError: function statement requires a name [Firefox] SyntaxError: Unexpected token ( [Chrome] Error Type: Syntax Error Cause of Error: Any function st
          
                
          JavaScript SyntaxError - Identifier starts immediately after numeric literal
          
                
          This JavaScript exception identifier starts immediately after a numeric literal occurs if an identifier starts with a number. Message: SyntaxError: Unexpected identifier after numeric literal (Edge) SyntaxError: identifier starts immediately after numeric literal (Firefox) SyntaxError: Unexpected number (Chrome) Error Type: SyntaxError Cause of Err
          
                
          JavaScript SyntaxError - Missing } after function body
          
                
          This JavaScript exception missing } after function body occurs if there is any syntactic mistyping while creating a function somewhere in the code. Closing curly brackets/parentheses must be incorrect order. Message: SyntaxError: Expected '}' (Edge) SyntaxError: missing } after function body (Firefox) Error Type: SyntaxError Cause of Error: Somewhe
          
                
          JavaScript SyntaxError - Missing } after property list
          
                
          This JavaScript exception missing } after property list occurs if there is a missing comma, or curly bracket in the object initializer syntax. Message: SyntaxError: Expected '}' (Edge) SyntaxError: missing } after property list (Firefox) Error Type: SyntaxError Cause of Error: Somewhere in the script, there is a missing curly bracket or missing com
          
                
          JavaScript SyntaxError - Redeclaration of formal parameter "x"
          
                
          This JavaScript exception redeclaration of formal parameter occurs if a variable name is a function parameter and also declared again inside the function body using a let assignment. Message: SyntaxError: Let/Const redeclaration (Edge) SyntaxError: redeclaration of formal parameter "x" (Firefox) SyntaxError: Identifier "x" has already been declared
          
                
          JavaScript SyntaxError - "0"-prefixed octal literals and octal escape sequences are deprecated
          
                
          This JavaScript exception 0-prefixed octal literals and octal escape sequences are deprecated works in strict mode only. For octal literals, the "0o" prefix can be used instead. Message: SyntaxError: Octal numeric literals and escape characters not allowed in strict mode (Edge) SyntaxError: "0"-prefixed octal literals and octal escape sequences are




    

          
                
          JavaScript SyntaxError - "x" is not a legal ECMA-262 octal constant
          
                
          This JavaScript warning 08 (or 09) is not a legal ECMA-262 octal constant that occurs if the literals 08 or 09 are used as a number. This occurs because these literals cannot be treated as an octal number. Message: Warning: SyntaxError: 08 is not a legal ECMA-262 octal constant. Warning: SyntaxError: 09 is not a legal ECMA-262 octal constant. Error
          
                
          JavaScript SyntaxError - Test for equality (==) mistyped as assignment (=)?
          
                
          This JavaScript warning test for equality (==) is mistyped as an assignment (=)? occurs if by assignment (=) is used in place of equality (==). Message: Warning: SyntaxError: test for equality (==) mistyped as assignment (=)? Error Type: SyntaxError: Warning which is reported only if javascript.options.strict preference is set to true. Cause of err
          
                
          JavaScript SyntaxError - Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
          
                
          This JavaScript warning Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead occurs if there is a source map syntax defined in a JavaScript source, Which has been depreciated. Message: Warning: SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead Warning: SyntaxError: Using //@ to indicate sourceMapp
          
                
          JavaScript SyntaxError – Octal literals are not allowed in strict mode
          
                
          If you put an octal literal in a code block that runs on strict, the result may be SyntaxError: Octal literals are not allowed in strict mode, since they can lead to unintended actions and confusion, numbers such as 0123 should never be strictly used, to understand this error better including possible causes, consider these examples. Understanding
          
                
          JavaScript SyntaxError – Invalid left-hand side in postfix operation
          
                
          A "SyntaxError: Invalid left-hand side in postfix operation" error occurs when JavaScript’s interpreter comes across an invalid expression that appears on the left hand side of a postfix increment (++) or decrement (--) operator, it is only variables or expressions which can take new values after this operation that are supposed to be used with pos
          
                
          JavaScript SyntaxError: Unterminated string literal
          
                
          This JavaScript error unterminated string literal occurs if there is a string that is not terminated properly. String literals must be enclosed by single (') or double (") quotes. Message:SyntaxError: Unterminated string constant (Edge)SyntaxError: unterminated string literal (Firefox)Error Type:SyntaxErrorWhat happened?There is a string in the cod
          
                
          JavaScript SyntaxError - Illegal character
          
                
          This JavaScript exception illegal character occurs if there is an invalid or unexpected token that doesn't belong there in the code. Understanding an errorAn "Unexpected token ILLEGAL" error signifies that there is an invalid character present within the code, in certain situations, JavaScript requires particular characters, however should one occu
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