JavaScript Basics

JavaScript Basics Summary (Hoisting, Strict Mode)

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Rules for Variable and Function Hoisting

• Variable hoisting: Execution still happens in order; variable declarations are hoisted but assignments are not.
• Function hoisting: The entire function body is hoisted to the top of its scope.
• Priority: Function hoisting > Variable hoisting.

console.log(a); // undefined
var a = 2;

foo(); // works normally
function foo() {
  console.log("Function hoisting succeeded");
}

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Using Strict Mode with use strict

What it does:

• Prevents creating accidental global variables;
• Disallows using undeclared variables, helping avoid memory leaks;
• Binds this to undefined by default instead of window.

function foo() {
  "use strict";
  console.log(this.a); // ❌ TypeError
}

var a = 2;
foo(); // in strict mode, this is undefined, so this.a cannot be read

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(function() {
  "use strict";
  foo(); // calling foo here doesn't change its default binding
})();

function foo() {
  console.log(this.a);
}

var a = 2;