Four ways JavaScript determines whether a string is contained in another string

One, IndexOf () 1. Definition

The IndexOf () method returns the index of the specified string for the first occurrence of the string object, and returns 1 if the specified value is not found. (Array same concept)

2. Syntax

str.indexOf(searchValue[, fromIndex])

• Searchvalue: The value that is being looked up in the string object.
• FromIndex: The index at which to start the lookup, which defaults to 0.

3. Example

let str = 'Hello, indexOf!';console.log(str.indexOf('Hello')); // 0console.log(str.indexOf('indexOf')); // 7console.log(str.indexOf('l')); // 2console.log(str.indexOf('l', 2)); // 2 加上开始查找的索引console.log(str.indexOf('l', 3)); // 3console.log(str.indexOf('e', 3)); // 10console.log(str.indexOf('l', 4)); // -1console.log(str.indexOf('world')); // -1

4. Pay attention to case sensitivity

let str = 'Hello, indexOf!';console.log(str.indexOf('e')); // 1console.log(str.indexOf('E')); // -1

II, includes () 1. Definition

The includes () method determines whether a string is contained in another string and returns True or false.

2. Syntax

str.includes(searchString[, position])

• SearchString: The string to search for.
• Position: Indicates the index from which to start the search, the default is 0.

3. Example

let str = 'Hello, includes!';console.log(str.includes('Hello')); // trueconsole.log(str.includes('includes')); // trueconsole.log(str.includes('hello')); // falseconsole.log(str.includes('Helle')); // falseconsole.log(str.includes('Helle', 1)); // falseconsole.log(str.includes('e', 2)); // true

Iii. StartsWith () 1. Definition

The StartsWith () method is used to determine whether a string is in the header of another string and returns True or false.

2. Syntax

str.startsWith(searchString[, position])

3. Example

let str = 'Hello, startsWith!';console.log(str.startsWith('Hello')); // trueconsole.log(str.startsWith('H')); // trueconsole.log(str.startsWith('h')); // falseconsole.log(str.startsWith('startsWith')); // falseconsole.log(str.startsWith('startsWith', 7)); // true

Iv. EndsWith () 1. Definition

The EndsWith () method is used to determine whether a string is at the end of another string and returns True or false.

2. Syntax

str.endsWith(searchString[, length])

• SearchString: The string to search for.
• Length: As a lookup string (str), the default is the length of the string itself.

3. Example

let str = 'Hello, endsWith!';console.log(str.endsWith('endsWith!')); // trueconsole.log(str.endsWith('EndsWith!')); // falseconsole.log(str.endsWith('Hello')); // falseconsole.log(str.endsWith('end', 10)); // true

Four ways JavaScript determines whether a string is contained in another string