Treat var as Block Scoped (block-scoped-var)

The block-scoped-var rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.

function doSomething() {
    if (true) {
        var build = true;
    }

    console.log(build);
}

Rule Details

This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.

The following patterns are considered problems:

/*eslint block-scoped-var: 2*/

function doSomething() {
    if (true) {
        var build = true;
    }

    console.log(build); /*error "build" used outside of binding context.*/
}

/*eslint block-scoped-var: 2*/

function doSomething() {
    if (true) {
        var build = true;  /*error "build" used outside of binding context.*/
    } else {
        var build = false; /*error "build" used outside of binding context.*/
    }
}

/*eslint block-scoped-var: 2*/

function doAnother() {
    try {
        var build = 1;
    } catch (e) {
        var f = build; /*error "build" used outside of binding context.*/
    }
}

The following patterns are not considered problems:

/*eslint block-scoped-var: 2*/

function doSomething() {
    var build;

    if (true) {
        build = true;
    }

    console.log(build);
}

/*eslint block-scoped-var: 2*/

function doSomething() {
    var build;

    if (true) {
        build = true;
    } else {
        build = false;
    }
}

Further Reading

Version

This rule was introduced in ESLint 0.1.0.

Resources