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Require or disallow padding lines between statements (padding-line-between-statements)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

This rule requires or disallows blank lines between the given 2 kinds of statements. Properly blank lines help developers to understand the code.

For example, the following configuration requires a blank line between a variable declaration and a return statement.

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: "var", next: "return" }
]*/

function foo() {
    var a = 1;

    return a;
}

Rule Details

This rule does nothing if no configurations are provided.

A configuration is an object which has 3 properties; blankLine, prev and next. For example, { blankLine: "always", prev: "var", next: "return" } means "one or more blank lines are required between a variable declaration and a return statement." You can supply any number of configurations. If a statement pair matches multiple configurations, the last matched configuration will be used.

{
    "padding-line-between-statements": [
        "error",
        { "blankLine": LINEBREAK_TYPE, "prev": STATEMENT_TYPE, "next": STATEMENT_TYPE },
        { "blankLine": LINEBREAK_TYPE, "prev": STATEMENT_TYPE, "next": STATEMENT_TYPE },
        { "blankLine": LINEBREAK_TYPE, "prev": STATEMENT_TYPE, "next": STATEMENT_TYPE },
        { "blankLine": LINEBREAK_TYPE, "prev": STATEMENT_TYPE, "next": STATEMENT_TYPE },
        ...
    ]
}
  • LINEBREAK_TYPE is one of the following.

    • "any" just ignores the statement pair.
    • "never" disallows blank lines.
    • "always" requires one or more blank lines. Note it does not count lines that comments exist as blank lines.
  • STATEMENT_TYPE is one of the following, or an array of the following.

    • "*" is wildcard. This matches any statements.
    • "block" is lonely blocks.
    • "block-like" is block like statements. This matches statements that the last token is the closing brace of blocks; e.g. { }, if (a) { }, and while (a) { }. Also matches immediately invoked function expression statements.
    • "break" is break statements.
    • "case" is case clauses in switch statements.
    • "cjs-export" is export statements of CommonJS; e.g. module.exports = 0, module.exports.foo = 1, and exports.foo = 2. This is a special case of assignment.
    • "cjs-import" is import statements of CommonJS; e.g. const foo = require("foo"). This is a special case of variable declarations.
    • "class" is class declarations.
    • "const" is const variable declarations, both single-line and multiline.
    • "continue" is continue statements.
    • "debugger" is debugger statements.
    • "default" is default clauses in switch statements.
    • "directive" is directive prologues. This matches directives; e.g. "use strict".
    • "do" is do-while statements. This matches all statements that the first token is do keyword.
    • "empty" is empty statements.
    • "export" is export declarations.
    • "expression" is expression statements.
    • "for" is for loop families. This matches all statements that the first token is for keyword.
    • "function" is function declarations.
    • "if" is if statements.
    • "iife" is immediately invoked function expression statements. This matches calls on a function expression, optionally prefixed with a unary operator.
    • "import" is import declarations.
    • "let" is let variable declarations, both single-line and multiline.
    • "multiline-block-like" is block like statements. This is the same as block-like type, but only if the block is multiline.
    • "multiline-const" is multiline const variable declarations.
    • "multiline-expression" is expression statements. This is the same as expression type, but only if the statement is multiline.
    • "multiline-let" is multiline let variable declarations.
    • "multiline-var" is multiline var variable declarations.
    • "return" is return statements.
    • "singleline-const" is single-line const variable declarations.
    • "singleline-let" is single-line let variable declarations.
    • "singleline-var" is single-line var variable declarations.
    • "switch" is switch statements.
    • "throw" is throw statements.
    • "try" is try statements.
    • "var" is var variable declarations, both single-line and multiline.
    • "while" is while loop statements.
    • "with" is with statements.

Examples

This configuration would require blank lines before all return statements, like the newline-before-return rule.

Examples of incorrect code for the [{ blankLine: "always", prev: "*", next: "return" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: "*", next: "return" }
]*/

function foo() {
    bar();
    return;
}

Examples of correct code for the [{ blankLine: "always", prev: "*", next: "return" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: "*", next: "return" }
]*/

function foo() {
    bar();

    return;
}

function foo() {
    return;
}

This configuration would require blank lines after every sequence of variable declarations, like the newline-after-var rule.

Examples of incorrect code for the [{ blankLine: "always", prev: ["const", "let", "var"], next: "*"}, { blankLine: "any", prev: ["const", "let", "var"], next: ["const", "let", "var"]}] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: ["const", "let", "var"], next: "*"},
    { blankLine: "any",    prev: ["const", "let", "var"], next: ["const", "let", "var"]}
]*/

function foo() {
    var a = 0;
    bar();
}

function foo() {
    let a = 0;
    bar();
}

function foo() {
    const a = 0;
    bar();
}

Examples of correct code for the [{ blankLine: "always", prev: ["const", "let", "var"], next: "*"}, { blankLine: "any", prev: ["const", "let", "var"], next: ["const", "let", "var"]}] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: ["const", "let", "var"], next: "*"},
    { blankLine: "any",    prev: ["const", "let", "var"], next: ["const", "let", "var"]}
]*/

function foo() {
    var a = 0;
    var b = 0;

    bar();
}

function foo() {
    let a = 0;
    const b = 0;

    bar();
}

function foo() {
    const a = 0;
    const b = 0;

    bar();
}

This configuration would require blank lines after all directive prologues, like the lines-around-directive rule.

Examples of incorrect code for the [{ blankLine: "always", prev: "directive", next: "*" }, { blankLine: "any", prev: "directive", next: "directive" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: "directive", next: "*" },
    { blankLine: "any",    prev: "directive", next: "directive" }
]*/

"use strict";
foo();

Examples of correct code for the [{ blankLine: "always", prev: "directive", next: "*" }, { blankLine: "any", prev: "directive", next: "directive" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: "directive", next: "*" },
    { blankLine: "any",    prev: "directive", next: "directive" }
]*/

"use strict";
"use asm";

foo();

This configuration would require blank lines between clauses in switch statements.

Examples of incorrect code for the [{ blankLine: "always", prev: ["case", "default"], next: "*" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: ["case", "default"], next: "*" }
]*/

switch (foo) {
    case 1:
        bar();
        break;
    case 2:
    case 3:
        baz();
        break;
    default:
        quux();
}

Examples of correct code for the [{ blankLine: "always", prev: ["case", "default"], next: "*" }] configuration:

/*eslint padding-line-between-statements: [
    "error",
    { blankLine: "always", prev: ["case", "default"], next: "*" }
]*/

switch (foo) {
    case 1:
        bar();
        break;

    case 2:

    case 3:
        baz();
        break;

    default:
        quux();
}

Compatibility

When Not To Use It

If you don't want to notify warnings about linebreaks, then it's safe to disable this rule.

Version

This rule was introduced in ESLint 4.0.0-beta.0.

Resources

© JS Foundation and other contributors
Licensed under the MIT License.
https://eslint.org/docs/rules/padding-line-between-statements