Disallow modifying variables that are declared using const (no-const-assign)

We cannot modify variables that are declared using const keyword. It will raise a runtime error.

Under non ES2015 environment, it might be ignored merely.

Rule Details

This rule is aimed to flag modifying variables that are declared using const keyword.

The following patterns are considered problems:

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

const a = 0;
a = 1;       /*error 'a' is constant.*/

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

const a = 0;
a += 1;      /*error 'a' is constant.*/

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

const a = 0;
++a;         /*error 'a' is constant.*/

The following patterns are not considered problems:

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

const a = 0;
console.log(a);

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

for (const a in [1, 2, 3]) { // `a` is re-defined (not modified) on each loop step.
    console.log(a);
}

/*eslint no-const-assign: 2*/
/*eslint-env es6*/

for (const a of [1, 2, 3]) { // `a` is re-defined (not modified) on each loop step.
    console.log(a);
}

When Not To Use It

If you don’t want to be notified about modifying variables that are declared using const keyword, you can safely disable this rule.

Version

This rule was introduced in ESLint 1.0.0-rc-1.

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