noConstAssign

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Diagnostic Category: lint/correctness/noConstAssign

JavaScript (and super languages)

Since: v1.0.0

Sources:

Same as: no-const-assign

Description

Prevents from having const variables being re-assigned.

Trying to assign a value to a const will cause an TypeError when the code is executed.

Examples

Invalid

const a = 1;
a = 4;

code-block.js:2:1 lint/correctness/noConstAssign  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Can’t assign a because it’s a constant
  
    1 │ const a = 1;
  > 2 │ a = 4;
      │ ^
    3 │ 
  
  ℹ This is where the variable is defined as constant
  
  > 1 │ const a = 1;
      │       ^
    2 │ a = 4;
    3 │ 
  
  ℹ Unsafe fix: Replace const with let if you assign it to a new value.
  
    1   │ - const·a·=·1;
      1 │ + let·a·=·1;
    2 2 │   a = 4;
    3 3 │

const a = 2;
a += 1;

code-block.js:2:1 lint/correctness/noConstAssign  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Can’t assign a because it’s a constant
  
    1 │ const a = 2;
  > 2 │ a += 1;
      │ ^
    3 │ 
  
  ℹ This is where the variable is defined as constant
  
  > 1 │ const a = 2;
      │       ^
    2 │ a += 1;
    3 │ 
  
  ℹ Unsafe fix: Replace const with let if you assign it to a new value.
  
    1   │ - const·a·=·2;
      1 │ + let·a·=·2;
    2 2 │   a += 1;
    3 3 │

const a = 1;
++a;

code-block.js:2:3 lint/correctness/noConstAssign  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Can’t assign a because it’s a constant
  
    1 │ const a = 1;
  > 2 │ ++a;
      │   ^
    3 │ 
  
  ℹ This is where the variable is defined as constant
  
  > 1 │ const a = 1;
      │       ^
    2 │ ++a;
    3 │ 
  
  ℹ Unsafe fix: Replace const with let if you assign it to a new value.
  
    1   │ - const·a·=·1;
      1 │ + let·a·=·1;
    2 2 │   ++a;
    3 3 │

const a = 1, b = 2;

a = 2;

code-block.js:3:1 lint/correctness/noConstAssign  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Can’t assign a because it’s a constant
  
    1 │ const a = 1, b = 2;
    2 │ 
  > 3 │ a = 2;
      │ ^
    4 │ 
  
  ℹ This is where the variable is defined as constant
  
  > 1 │ const a = 1, b = 2;
      │       ^
    2 │ 
    3 │ a = 2;
  
  ℹ Unsafe fix: Replace const with let if you assign it to a new value.
  
    1   │ - const·a·=·1,·b·=·2;
      1 │ + let·a·=·1,·b·=·2;
    2 2 │   
    3 3 │   a = 2;

Valid

const a = 10;
let b = 10;
b = 20;

How to configure

{
  "linter": {
    "rules": {
      "correctness": {
        "noConstAssign": "error"
      }
    }
  }
}