JS string interception, conversion of strings and numbers

JS get the last character of a string

Method 1: String.charAt ( String.length - 1)

const str = "123456";
console.log(str.charAt(str.length - 1)); // 6

Method 2: String.substring ( String.length - 1)

const str = "123456";
console.log(str.substring(str.length - 1)); // 6

JS intercepts the string after a specific character

indexOf() The index of the first occurrence of a character from left to right: String .indexOf("-")

const str = "2022-11-19";
console.log(str.substring(str.indexOf("-") + 1)); // 11-19

lastIndexOf() The index of the first occurrence of a character from right to left: String .lastIndexOf("-")

const str = "2022-11-19";
console.log(str.substring(str.lastIndexOf("-") + 1)); // 19

JS removes the first N characters in a string

Remove the first three digits of the string: String .slice(3)

const str = "12345678";
console.log(str.slice(3)); // 45678

JS removes the last N characters in the string

Remove the last two digits of the string: String .slice(0, -2)

const str = "12345678";
console.log(str.slice(0, -2)); // 123456

JS adds a specific string to the string

Insert a specific string after the 3rd digit of the string: String.slice(0, 3) + "newStr" + String.slice(3)

const str = "123456";
console.log(str.slice(0, 3) + "newStr" + str.slice(3)); // 123newStr456

JS intercepts the first N characters of a string

Intercept the first five digits of the string: String.substring(0, 5)

const str = "12345678";
console.log(str.substring(0, 5)); // 12345

JS intercepts N characters after the string

Intercept the last three digits of the string: String.substring(String.length - 3, String.length)

const str = "12345678";
console.log(str.substring(str.length - 3, str.length)); // 678

JS number to string

Method 1: Number.toString()

const num = 12345;
console.log(num.toString()); // 12345

Method 2 (number + any string): Number + ""

const num = 12345;
console.log(num + ""); // 12345

JS string to number

Method 1 (round down): parseInt(Number)

const num = "123.75";
console.log(parseInt(num)); // 123

Method 2 (reserve decimals): parseFloat(Number)

const num = "123.75";
console.log(parseFloat(num)); // 123.75

Method 3 (mandatory type conversion [reserve decimals]): Number(Number)

const num = "123.75";
console.log(Number(num)); // 123.75