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JavaScript TypeError – Invalid assignment to const “X”
  • Last Updated : 31 Jul, 2020

This JavaScript exception invalid assignment to const occurs if a user tries to change a constant value. Const declarations in JavaScript can not be re-assigned or re-declared.

Message:

TypeError: invalid assignment to const "x" (Firefox)
TypeError: Assignment to constant variable. (Chrome)
TypeError: Assignment to const (Edge)
TypeError: Redeclaration of const 'x' (IE)

Error Type:

TypeError

Cause of Error: A const value in JavaScript is changed by the program which can not be altered during normal execution. 

Example 1: In this example, the value of the variable(‘GFG’) is changed, So the error has occurred.



HTML




<script>
    const GFG = "This is GFG";
    // Error here
    GFG = "This is GeeksForGeeks"; 
</script>

Output(in console):

TypeError: Assignment to const

Example 2: In this example, the value of the object(‘GFG_Obj’) is changed, So the error has occurred.

HTML




<script>
    const GFG_Obj = {key: 'val1'};
    // Error here
    GFG_Obj = {key: 'val2'}; 
</script>

Output:

TypeError: Assignment to const
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