Summary of commonly used string usage methods in Javascript-JS Tutorial-php.cn

Summary of commonly used string usage methods in Javascript

黄舟

Release： 2017-03-20 14:58:31

Original

1500 people have browsed it

This article mainly introduces the common usage methods related to string in Javascript. Has very good reference value. Let’s take a look at it with the editor

I was just reading the Javascript Rhino book and saw the section on strings. I don’t have much exposure to this aspect in my daily work, so I thought I would sort it out in case I need it. .

One of the built-in functions of Javascript is string concatenation. If you use '+' to connect two numbers, it means adding the two numbers. But if used in a string, it means that the second character is added after the first character.

var num=1+2;
console.log(num);
var msg=&#39;hello&#39;+&#39;world&#39;;
console.log(msg);

Copy after login

For strings, in addition to the length attribute, there are many other useful attributes, such as:

var str=&#39;hello,world&#39;;
console.log(str.length);
console.log(str.charAt(0)); //第一个字符 
console.log(str.charAt(str.length-1)); // 最后一个字符 
//substring(starti,endi), 截取 字符串 起始startistartii， 到endi结束，且含头不含尾，没有
// 如果第二个参数没有， 就默认截取到最后一个。  
console.log(str.substring(1,4));
console.log(str.substring(1));
//用法同上，为负数时，就是倒数开始算，一个参数含义是倒数几个。
console.log(str.slice(1,4));
console.log(str.slice(-3));
//字符‘l&#39;首次出现的位置 
console.log(str.indexOf(&#39;l&#39;));
//字符‘l&#39;最后一次出现的位置 
console.log(str.lastIndexOf(&#39;l&#39;));
//在位置下标3之后，首次出现的位置 
console.log(str.indexOf(&#39;l&#39;,3));
//用‘，&#39;分割为字符串
console.log(str.split(&#39;,&#39;));
// 把str中的小写h换成大写H
console.log(str.replace(&#39;h&#39;,&#39;H&#39;));
//讲字符串转化为大写
console.log(str.toUpperCase());

Copy after login

Tips: The string itself is fixed in JavaScript. The above methods will return a new string value and will not affect the value of str itself.

It is worth noting that in ES6 , adds many new methods to strings, such as:

var s = &#39;Hello world!&#39;;
// 返回布尔值，表示参数字符串是否在源字符串中的头部
console.log(s.startsWith(&#39;Hello&#39;)) // true
//endsWith()：返回布尔值，表示参数字符串是否在源字符串的尾部
console.log(s.endsWith(&#39;!&#39;)) // true
// includes()返回布尔值，表示是否找到了参数字符串
console.log(s.includes(&#39;o&#39;)) // true

Copy after login

The above three methods all support the second parameter, which indicates the position to start search

var s = &#39;Hello world!&#39;;
console.log(s.startsWith(&#39;world&#39;, 6)) // true
console.log(s.endsWith(&#39;Hello&#39;, 5))// true
console.log(s.includes(&#39;Hello&#39;, 6)) // false

Copy after login

Tip: endsWith behaves differently than the other two methods. It targets the first n characters, while the other two methods target from the nth position until the end of the string.
The repeat method returns a new string, which means repeating the original string n times.

console.log(&#39;x&#39;.repeat(3)) // "xxx"
console.log(&#39;hello&#39;.repeat(2)) // "hellohello"
console.log(&#39;na&#39;.repeat(0)) // ""

Copy after login

If the parameter is a decimal, it will be rounded.

console.log(&#39;na&#39;.repeat(2.9)) // "nana"
//如果repeat的参数是负数或者Infinity，会报错。
console.log(&#39;na&#39;.repeat(Infinity))
// RangeError
console.log(&#39;na&#39;.repeat(-1))
// RangeError

Copy after login

However, if the parameter is a decimal between 0 and -1, it is equivalent to 0, because the rounding operation will be performed first. A decimal between 0 and -1 is equal to -0 after rounding, and repeat is regarded as 0.

console.log(&#39;na&#39;.repeat(-0.9)) // ""
//参数NaN等同于0
console.log(&#39;na&#39;.repeat(NaN)) // "
//如果repeat的参数是字符串，则会先转换成数字
console.log(&#39;na&#39;.repeat(&#39;na&#39;)) // ""
console.log(&#39;na&#39;.repeat(&#39;3&#39;)) // "nanana"

Copy after login

ES2017 introduces the function of string completion length. If a string is not long enough, it will be completed at the head or tail. padStart() is used for head completion, padEnd() is used for tail completion

//padStart和padEnd一共接受两个参数，第一个参数用来指定字符串的最小长度，第二个参数是用来补全的字符串。
console.log(&#39;x&#39;.padStart(5, &#39;ab&#39;)) // &#39;ababx&#39;
console.log(&#39;x&#39;.padStart(4, &#39;ab&#39;)) // &#39;abax&#39;
console.log(&#39;x&#39;.padEnd(5, &#39;ab&#39;)) // &#39;xabab&#39;
console.log(&#39;x&#39;.padEnd(4, &#39;ab&#39;)) // &#39;xaba&#39;
//如果原字符串的长度，等于或大于指定的最小长度，则返回原字符串。
console.log(&#39;xxx&#39;.padStart(2, &#39;ab&#39;)) // &#39;xxx&#39;
console.log(&#39;xxx&#39;.padEnd(2, &#39;ab&#39;)) // &#39;xxx&#39;
//如果用来补全的字符串与原字符串，两者的长度之和超过了指定的最小长度，则会截去超出位数的补全字符串。
consoe.log(&#39;abc&#39;.padStart(10, &#39;0123456789&#39;))
// &#39;0123456abc&#39;
//如果省略第二个参数，默认使用空格补全长度。
console.log(&#39;x&#39;.padStart(4)) // &#39; x&#39;
console.log(&#39;x&#39;.padEnd(4)) // &#39;x &#39;
//padStart的常见用途是为数值补全指定位数。下面代码生成10位的数值字符串。
console.log(&#39;1&#39;.padStart(10, &#39;0&#39;) )// "0000000001"
console.log(&#39;12&#39;.padStart(10, &#39;0&#39;)) // "0000000012"
console.log(&#39;123456&#39;.padStart(10, &#39;0&#39;)) // "0000123456"
//另一个用途是提示字符串格式。
console.log(&#39;12&#39;.padStart(10, &#39;YYYY-MM-DD&#39;)) // "YYYY-MM-12"
console.log(&#39;09-12&#39;.padStart(10, &#39;YYYY-MM-DD&#39;))// "YYYY-09-12"

Copy after login

The above is the detailed content of Summary of commonly used string usage methods in Javascript. For more information, please follow other related articles on the PHP Chinese website!