Strict Mode in JavaScript
From the JavaScript cheat sheet · Hoisting & Strict Mode · verified Jul 2026
Strict Mode
Using strict mode for safer JavaScript
javascript
// Enable strict mode
'use strict';
// Prevents accidental globals
// mistypedVariable = 17; // Error
// Prevents duplicate parameters
// function sum(a, a, c) {} // Error
// Makes eval safer
// eval has its own scope in strict mode💡 Always use strict mode to catch common mistakes
⚡ Modules and classes are automatically in strict mode
📌 Strict mode must be first statement in script or function
🔥 Strict mode makes this undefined in regular functions
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