useConst

诊断类别：lint/style/useConst

¥Diagnostic Category: lint/style/useConst

JavaScript (and super languages)

自从：v1.0.0

¥Since: v1.0.0

来源：

¥Sources:

与以下相同：prefer-const

¥Same as: prefer-const

要求仅分配一次的变量进行 const 声明。

¥Require const declarations for variables that are only assigned once.

已初始化且从未重新分配的变量和仅分配一次的变量可以声明为 const。

¥Variables that are initialized and never reassigned and variables that are only assigned once can be declared as const.

示例

¥Examples

无效

¥Invalid

let a = 3;
console.log(a);

code-block.js:1:1 lint/style/useConst  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This let declares a variable that is only assigned once.
  
  > 1 │ let a = 3;
      │ ^^^
    2 │ console.log(a);
    3 │ 
  
  ℹ ‘a’ is never reassigned.
  
  > 1 │ let a = 3;
      │     ^
    2 │ console.log(a);
    3 │ 
  
  ℹ Safe fix: Use const instead.
  
    1   │ - let·a·=·3;
      1 │ + const·a·=·3;
    2 2 │   console.log(a);
    3 3 │

// `a` is redefined (not reassigned) on each loop step.
for (let a of [1, 2, 3]) {
    console.log(a);
}

code-block.js:2:6 lint/style/useConst  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This let declares a variable that is only assigned once.
  
    1 │ // a is redefined (not reassigned) on each loop step.
  > 2 │ for (let a of [1, 2, 3]) {
      │      ^^^
    3 │     console.log(a);
    4 │ }
  
  ℹ ‘a’ is never reassigned.
  
    1 │ // a is redefined (not reassigned) on each loop step.
  > 2 │ for (let a of [1, 2, 3]) {
      │          ^
    3 │     console.log(a);
    4 │ }
  
  ℹ Safe fix: Use const instead.
  
    1 1 │   // a is redefined (not reassigned) on each loop step.
    2   │ - for·(let·a·of·[1,·2,·3])·{
      2 │ + for·(const·a·of·[1,·2,·3])·{
    3 3 │       console.log(a);
    4 4 │   }

// `a` is redefined (not reassigned) on each loop step.
for (let a in [1, 2, 3]) {
    console.log(a);
}

code-block.js:2:6 lint/style/useConst  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This let declares a variable that is only assigned once.
  
    1 │ // a is redefined (not reassigned) on each loop step.
  > 2 │ for (let a in [1, 2, 3]) {
      │      ^^^
    3 │     console.log(a);
    4 │ }
  
  ℹ ‘a’ is never reassigned.
  
    1 │ // a is redefined (not reassigned) on each loop step.
  > 2 │ for (let a in [1, 2, 3]) {
      │          ^
    3 │     console.log(a);
    4 │ }
  
  ℹ Safe fix: Use const instead.
  
    1 1 │   // a is redefined (not reassigned) on each loop step.
    2   │ - for·(let·a·in·[1,·2,·3])·{
      2 │ + for·(const·a·in·[1,·2,·3])·{
    3 3 │       console.log(a);
    4 4 │   }

let a;
a = 0;

code-block.js:1:1 lint/style/useConst ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This let declares a variable that is only assigned once.
  
  > 1 │ let a;
      │ ^^^
    2 │ a = 0;
    3 │ 
  
  ℹ ‘a’ is only assigned here.
  
    1 │ let a;
  > 2 │ a = 0;
      │ ^
    3 │

let a = 3;
{
    let a = 4;
    a = 2;
}

code-block.js:1:1 lint/style/useConst  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This let declares a variable that is only assigned once.
  
  > 1 │ let a = 3;
      │ ^^^
    2 │ {
    3 │     let a = 4;
  
  ℹ ‘a’ is never reassigned.
  
  > 1 │ let a = 3;
      │     ^
    2 │ {
    3 │     let a = 4;
  
  ℹ Safe fix: Use const instead.
  
    1   │ - let·a·=·3;
      1 │ + const·a·=·3;
    2 2 │   {
    3 3 │       let a = 4;

有效

¥Valid

let a = 2;
a = 3;
console.log(a);

let a = 1, b = 2;
b = 3;

let a;
a; // the variable is read before its assignement
a = 0;

useConst

示例

无效

有效

相关链接