let

See also

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let

• https://stackoverflow.com/questions/37916940/why-was-the-name-let-chosen-for-block-scoped-variable-declarations-in-javascri

Definition

The let statement declares a block-scoped local variable, optionally initializing it to a value.

let allows you to declare variables that are limited to the scope of a block statement, or expression on which it is used, unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope.

The other difference between var and let is that the latter is initialized to a value only when a parser evaluates it (see below).

Just like const the let does not create properties of the window object when declared globally (in the top-most scope).

An explanation of why the name “let” was chosen can be found here .

History

See also

• https://stackoverflow.com/questions/37916940/why-was-the-name-let-chosen-for-block-scoped-variable-declarations-in-javascri

Let is a mathematical statement that was adopted by early programming languages like Scheme and Basic.

Variables are considered low level entities not suitable for higher levels of abstraction, thus the desire of many language designers to introduce similar but more powerful concepts like in Clojure, F#, Scala, where let might mean a value, or a variable that can be assigned, but not changed, which in turn lets the compiler catch more programming errors and optimize code better.

JavaScript has had var from the beginning, so they just needed another keyword, and just borrowed from dozens of other languages that use let already as a traditional keyword as close to var as possible, although in JavaScript let creates block scope local variable instead.