Block scope: let declaration

let restricts the scope of the variable to the current block

comparing var with let

WHEN using var for declaring a variable THEN the scope of the variable is the surrounding function

//: {"jskatas": {"terms": ["block", "scope"]}} if (true) { let varX = true; } assert.equal(varX, true);

WHEN declaring a variable using let THEN the scope is limited to the surrounding block (enclosed in { and })

if (true) { var letX = true; } assert.throws(() => letX, ReferenceError);

using let

WHEN using let in a for loop THEN the variable is only "visible" inside this loop

let obj = {x: 1}; for (var key in obj) {} assert.throws(() => key, ReferenceError);

WHEN embedding a let variable in a block (using curly braces) THEN the variable is not "visible" outside of it

{ var letX = true; } assert.throws(() => letX, ReferenceError);

WHEN declaring a variable with let without a value THEN this variable has the value undefined

let variable = 42; assert.strictEqual(variable, undefined);

Related Katas

Block scope

• let declaration
• const declaration

Difficulty Level

BEGINNER

First Published

23 March 2015

Stats

5 tests to solve