SyntaxError: "use strict" not allowed in function with non-simple parameters

The JavaScript exception " 'use strict' not allowed in function" occurs when a "use strict" directive is used at the top of a function with 默认参数 , rest parameters ,或 destructuring parameters .

Message

Edge:
Cannot apply strict mode on functions with non-simple parameter list
Firefox:
SyntaxError: "use strict" not allowed in function with default parameter
SyntaxError: "use strict" not allowed in function with rest parameter
SyntaxError: "use strict" not allowed in function with destructuring parameter
Chrome:
SyntaxError: Illegal 'use strict' directive in function with non-simple parameter list
					

Error type

SyntaxError .

What went wrong?

A "use strict" directive is written at the top of a function that has one of the following parameters:

A "use strict" directive is not allowed at the top of such functions per the ECMAScript specification.

范例

Function statement

In this case, the function sum has default parameters a=1 and b=2 :

function sum(a = 1, b = 2) {
  // SyntaxError: "use strict" not allowed in function with default parameter
  'use strict';
  return a + b;
}
					

If the function should be in 严格模式 , and the entire script or enclosing function is also okay to be in strict mode, you can move the "use strict" directive outside of the function:

'use strict';
function sum(a = 1, b = 2) {
  return a + b;
}
					

Function expression

A function expression can use yet another workaround:

var sum = function sum([a, b]) {
  // SyntaxError: "use strict" not allowed in function with destructuring parameter
  'use strict';
  return a + b;
};
					

This can be converted to the following expression:

var sum = (function() {
  'use strict';
  return function sum([a, b]) {
    return a + b;
  };
})();
					

Arrow function

If an arrow function needs to access the this variable, you can use the arrow function as the enclosing function:

var callback = (...args) => {
  // SyntaxError: "use strict" not allowed in function with rest parameter
  'use strict';
  return this.run(args);
};
					

This can be converted to the following expression:

var callback = (() => {
  'use strict';
  return (...args) => {
    return this.run(args);
  };
})();
					

另请参阅

Metadata

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    62. TypeError: cyclic object value
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    64. TypeError: invalid Array.prototype.sort argument
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    69. TypeError: variable "x" redeclares argument
    70. URIError: malformed URI sequence
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    72. Warning: 08/09 is not a legal ECMA-262 octal constant
    73. Warning: Date.prototype.toLocaleFormat is deprecated
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    75. Warning: String.x is deprecated; use String.prototype.x instead
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    77. Warning: unreachable code after return statement
  13. 杂项
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