Rule: no-use-before-declare

Disallows usage of variables before their declaration.

This rule is primarily useful when using the var keyword since the compiler will automatically detect if a block-scoped let and const variable is used before declaration. Since most modern TypeScript doesn’t use var, this rule is generally discouraged and is kept around for legacy purposes. It is slow to compute, is not enabled in the built-in configuration presets, and should not be used to inform TSLint design decisions.

Notes:

Config

Not configurable.

Config examples

"no-use-before-declare": true

Schema

null

Code examples:

"rules": { "no-use-before-declare": true }

var hello = 'world';
var foo;

console.log(hello, foo, capitalize(hello));
// 'world', undefined, 'WORLD'

function capitalize(val) {
    return val.toUpperCase();
}

import { default as foo1 } from "./lib";
import foo2 from "./lib";
import _, { map, foldl } from "./underscore";
import * as foo3 from "./lib";
import "./lib";

function declaredImports() {
    console.log(foo1);
    console.log(foo2);
    console.log(foo3);
    map([], (x) => x);
}

console.log(hello, foo);

var hello = 'world';
var foo;

function undeclaredImports() {
    console.log(foo1);
    console.log(foo2);
    console.log(foo3);
    map([], (x) => x);
}

import { default as foo1 } from "./lib";
import foo2 from "./lib";
import _, { map, foldl } from "./underscore";
import * as foo3 from "./lib";
import "./lib";