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JavaScript SyntaxError – Test for equality (==) mistyped as assignment (=)?

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  • Last Updated : 19 Aug, 2020
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This JavaScript warning test for equality (==) mistyped as 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 error: There is an assignment (=) used in place of equality (==) in the code. 

Example 1: In this example, the ‘=’ is used in place of ‘==’. So the error has occurred.

HTML




<script>
if (a = b) { // Error here
  // do something
}
</script>

Output:

Warning: SyntaxError: test for equality (==) 
mistyped as assignment (=)?

Example 2:  In this example, the ‘=’ is used in place of ‘==’. So the error has occurred.

HTML




<script>
    var a = 5;
    var b = 4;
    var c = 5;
    if (b = c) {
      // do something
    } else if (a = c) {
      // do something
    }
</script>

Output:

Warning: SyntaxError: test for equality (==) 
mistyped as assignment (=)?
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