[数据类型]string字符串

定义

var str = '';
var str = new String('');
var str = String('');
typeof('hello')  //"string"

计算字符串长度

str.length 
// null  undefine

读取指定

'error'['2']
"r"
'error'[2]
"r"
'error'.2
VM316:1 Uncaught SyntaxError: Unexpected number

字符索引号—匹配

str.indexOf(searchValue[, fromIndex])
str.lastIndexOf(searchValue[, fromIndex])
//ex
var str = '2-3-21-2'
str.indexOf('2')  //0
str.lastIndexOf('2')  //7
str.search(regexp)
？？？？？？？？？？？
str.endsWith(searchString[, length])
'Hello word!'.endsWith('!')  //true
'Hello word!'.endsWith('wo', 8)  //true
'Hello word!'.endsWith('wo', 7)  //false
str.includes(searchString[, position])  
'Hello word!'.includes('hello')   //false
'Hello word!'.includes('ello', 1)  //true
'Hello word!'.includes('ello', 4)   //false
str.match(regexp)
？？？？？？？？？？？？

截取

str.slice(beginIndex[, endIndex])
'hello'.slice(1)   //"ello"
'hello'.slice(1,4)   //"ell"
str.substr(start[, length])
'Hello'.substr(1)  //"ello"
'Hello'.substr(1,2)  //"el"
str.substring(indexStart[, indexEnd])(不推荐)
'Hello'.substring(1)   //"ello"
'Hello'.substring(1,4)  //"ell"
//slice、substring区别：slice中的index可以为负数

拼接

str.concat(string2[, string3, ..., stringN])
'Hello'.concat(' Word!')  //"Hello Word!"
str.padEnd(targetLength [, padString])
'hello'.padEnd(6);  //"hello "
'hello'.padEnd(14, ' word!');  //"hello word! wo"
str.padStart(targetLength [, padString])
'word'.padStart(6);  //"  word"
'word'.padStart(12, 'Hello ');  //"Hello Heword"
str.repeat(count);
'Hello'.repeat(1.5)  //"Hello"
'Hello'.repeat(2)   //"HelloHello"

格式化

'Hello'.toUpperCase() //"HELLO"
'Hello'.toLowerCase()  //"hello"
'  Hello  '.trim() //"Hello"
'  Hello  '.trimLeft()  //"Hello  "
'  Hello  '.trimRight()  //"  Hello"
str.replace(regexp|substr, newSubstr|function)
？？？？？？？？？？？？？？

填充函数

'bcd'.padStart(4)//    " bcd"
'bcd'.padEnd(4)//    "bcd "
'bcd'.padLeft(4)//    " bcd"
'bcd'.padRight(4)//    "bcd "

场景

'0.0'.padStart(10)      //    "       0.0"
'188,000.0'.padStart(10)//    " 188,000.0"
'0.0'.padStart(10, '-')      // "-------0.0"

charAt

  /*==============string=================*/
    var str1 = "abcdefgc";
    console.log(str1.length);  //8
    /*charAt()  固定位置的字符  默认是首字母 0开始计数*/
    console.log(str1.charAt());  //a
    console.log(str1.charAt(0));  //a
    console.log(str1.charAt(2));  //c
    /*str[num]  支持IE7以上版本*/
    //console.log(str1[]);  //error
    console.log(str1[0]);  //a
    console.log(str1[2]);  //c
    /*charCodeAt()  固定位置的字符编码 */
    console.log(str1.charCodeAt());  //97
    console.log(str1.charCodeAt(0));  //97
    console.log(str1.charCodeAt(2));  //99

sting == arr

//转【】
str.split([separator[, limit]])
var str = '2-3-21-2'
str.split("-"); //["2", "3", "21", "2"]
str.indexOf('2')  //0
str.lastIndexOf('2')  //7
//转str
[2,3].join(",") //    "2,3"
Object.values('err')
// (3) ["e", "r", "r"]
Object.keys('err')
// (3) ["0", "1", "2"]

返回index的utf-16编码

js内部utf-16存储
character = str.charAt(index);
'hello'.charAt(1); \\ "e"
'\u0068\u0065\u006c\u006c\u006f'.charAt(1);    \\"e"

转标签

'hello'.sub() //"<sub>hello</sub>"
'hello'.sup() //"<sup>hello</sup>"

replace/replaceAll替换

返回一个替换以后的新字符串。

// 替换第一个
'23-21312-dwe-342-3dsd'.replace('-', '')
"2321312-dwe-342-3dsd"
// replaceAll， 替换全部
'23-21312-dwe-342-3dsd'.replace(/-/g, '')
"2321312dwe3423dsd"

插入

function insert(oldStr, insertPos, insertStr ) {
    oldStr = oldStr.slice(0, insertPos) + insertStr + oldStr.slice(insertPos)
  return oldStr;
}
// test
var b = '112233'
insert(b, 2, '88')
"11882233"