1'use strict';
2
3// This will throw an error in strict mode
4x = 5; // ReferenceError: x is not defined
5
6// Correct way
7let x = 5;

1'use strict';
2
3// Your code here

1// This file is already in strict mode
2import React from 'react';
3import { useState } from 'react';
4
5function MyComponent() {
6  // Code here is automatically in strict mode
7}

1function myFunction() {
2  'use strict';
3  // This function runs in strict mode
4}

1// Without strict mode - creates global variable
2mistypedVariable = 17; // no error
3
4// With strict mode
5('use strict');
6mistypedVariable = 17; // ReferenceError: mistypedVariable is not defined

1// Without strict mode
2const obj = { name: 'test' };
3Object.defineProperty(obj, 'age', { writable: false });
4obj.age = 25; // Silently fails
5
6// With strict mode
7('use strict');
8obj.age = 25; // TypeError: Cannot assign to read only property 'age'

1// Without strict mode - allowed
2function sum(a, a, c) {
3  return a + c;
4}
5
6// With strict mode - error
7('use strict');
8function sum(a, a, c) {
9  // SyntaxError: Duplicate parameter name not allowed
10  return a + c;
11}

1// Without strict mode
2var num = 010; // 8 in octal
3
4// With strict mode
5('use strict');
6var num = 010; // SyntaxError: Octal literals are not allowed

1// Without strict mode
2function test() {
3  console.log(this); // references global object
4}
5
6// With strict mode
7('use strict');
8function test() {
9  console.log(this); // undefined
10}

1// Without strict mode
2var x = 42;
3delete x; // Silently fails
4
5// With strict mode
6('use strict');
7var x = 42;
8delete x; // SyntaxError: Delete of an unqualified identifier

1// Without strict mode
2var implements = 42; // Works
3
4// With strict mode
5('use strict');
6var implements = 42; // SyntaxError: implements is a reserved word

1// Without strict mode
2with (Math) {
3  x = cos(2); // Works
4}
5
6// With strict mode
7('use strict');
8with (Math) {
9  // SyntaxError: Strict mode code may not include a with statement
10  x = cos(2);
11}