What does index mean in js

index in JavaScript represents the position of an element in an array or string, starting from 0. Use the index to access and modify elements through square bracket notation. Note that the index must be a non-negative integer and accessing a non-existent index will result in an error.

index means in JavaScript

index in JavaScript is the index of the position of an element in an array or string . It starts at 0, which means the first element has index 0, the second element has index 1, and so on.

How to use index

You can access elements in an array or string using square bracket notation, where the index specifies the position of the element to be accessed. For example:

const array = [1, 2, 3, 4, 5];
console.log(array[0]); // 输出：1
console.log(array[2]); // 输出：3

For strings, indexing also works the same way:

const str = "Hello";
console.log(str[0]); // 输出：H
console.log(str[3]); // 输出：l

Modify elements

You can also use indexing to modify arrays or elements in the string. For example:

const array = [1, 2, 3, 4, 5];
array[2] = 10;
console.log(array); // 输出：[1, 2, 10, 4, 5]

For strings, individual characters cannot be modified, but the entire string can be replaced:

const str = "Hello";
str = "World";
console.log(str); // 输出：World

Note

• The index must is a non-negative integer.
• Accessing a non-existing index will result in an error.
• For sparse arrays (where the value at some index is undefined), index still starts at 0, but accessing a non-existent index does not cause an error.

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