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Chapter XXIII · Error Handling

Strict Mode

Strict mode (`'use strict'`) opts a script or function into a stricter parsing and error-handling variant of JavaScript.

01 How It Works

Think of a safety inspector enforcing strict compliance rules on a factory workshop floor.

Strict mode catches silent developer mistakes, throws errors for unsafe actions (like global accidental variable assignments), and disables insecure features.

example.js
"use strict";
x = 10; // ReferenceError: x is not defined

  1. 1. Add `'use strict';` at the top of a script or function body.

  2. 2. Engine enforces strict validation rules.

  3. 3. Throws exceptions for unsafe coding practices.

02 Practical Example

Here is how you might see this concept applied in real-world code:

practical.js
"use strict";
function secure() {
  let eval = 17; // SyntaxError in strict mode
}

Key Takeaway

Always use strict mode to write cleaner, safer, and more robust JavaScript code.

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