第八章 字符串

1 增加

1-1 concat 拼接

var a = 'hello'
var b = "world"
console.log(a.concat(b));

2 查询

2-1 slice(startIndex,endIndex)

2-2 substr(index,length)

注意：第二个参数 为长度

2-3 substring(startIndex,endIndex)

var arr = "hello"
console.log(arr.slice(0)); // hello
console.log(arr.slice(0,3)); // hel
console.log(arr.substr(0,3)); // hel
console.log(arr.substring(0,2)); // he

2-4 charAt(index) 根据下标查找对应的值

var str = "hello"
console.log(str.charAt(1)); // e

2-5 indexOf(value) 根据值查找对应的下标 找不到返回-1

var arr = "hello";
console.log(arr.indexOf('e')); // 1

2-6 search(value) 根据值查找对应的下标 找不到返回-1

 var str = "你是谁"
 var index = str.search("她")
 console.log(index);   //  -1

2-7 includes 是否包含某位(多位)字符 返回boolean

var arr = "hello"
console.log(arr.includes("eh")); //false

2-8 match(value) 返回匹配的字符串，返回的是数组

var str ="hello"
var arr = str.match("l")
console.log(arr);  // ["l", index: 2, input: "hello", groups: undefined]
// 找不到返回 null

3 length 字符串的长度

var str = "hello"
console.log(str.length);
var s = "故事的结尾，心上人"
console.log(handleStr(s));
function handleStr(value){
  if(value.length>5){
    return value.slice(0,5)+"..."
  }
  return value
}

4 其他方法

4-1 split( ) 将字符串分割成字符串数组

var str = "hello"
console.log(str.split()); // 将字符串转为数组 ["hello"]
console.log(str.split("")); // ["h","e","l","l","o"]
console.log(str.split("e"));// ["h","llo"]

4-2 replace( ) 替换字符串

var str = "hello"
console.log(str.replace("l","*"));  //  he*lo

4-3 search()

//返回下标值

4-4 match

//返回数组

4-5 trim( ) 去除字符串前后的空格

// 正则表达式：  /^\s+|\s+$/g  
var str = "   hello   ";
var arr = []
arr.push(str.trim())
console.log(arr)