【前端学习笔记02】JavaScript字符串、数组的一些操作方法

字符串操作：

//str.length
"micromajor".length  // 10

//str.charAt()
"micromajor".charAt(0)   // "m"
"micromajor".charAt(100) // ""

//str.indexOf()
"micro-major".indexOf("-")     // 5
"micro-major-web".indexOf("-") // 5
"micro-major".indexOf("major") // 6
"micromajor".indexOf("-")      // -1

//str.search()
"micromajor163".search(/[0-9]/) // 10
"micromajor163".search(/[A-Z]/) // -1

//str.match
"micromajor163".match(/[0-9]/) // ["1"]
"micromajor163".match(/[0-9]/g)// ["1","6","3"]
"micromajor163".match(/[A-Z]/) // null

//str.replace(' ',' ');
"micromajor163".replace("163","###")  // "micromajor###"
"micromajor163".replace(/[0-9]/,"#")  // "micromajor#63"
"micromajor163".replace(/[0-9]/g,"#") // "micromajor###"
"micromajor163".replace(/[0-9]/g,"")  // "micromajor"

//str.substring
"micromajor".substring(5,7)  // "ma"
"micromajor".substring(5)    // "major"

//str.slice() 可传入负数
"micromajor".slice(5,7)   // "ma"
"micromajor".slice(5)     // "major"
"micromajor".slice(1,-1)  // "icromajo"
"micromajor".slice(-3)    // "jor"

//str.substr()
"micromajor".substr(5,2)  // "ma"
"micromajor".substr(5)    // "major"

//str.split();
"micro major".split(" ")     // ["micro","major"]
"micro major".split(" ",1)   // ["micro"]
"micro2major".split(/[0-9]/) // ["micro","major"]

//str.toLowerCase();
"MicroMajor".toLowerCase()  // "micromajor"
//str.toUpperCase();
"MicroMajor".toUpperCase()  // "MICROMAJOR"

//字符串拼接
"0571" + "-" + "88888888"  // "0571-88888888"

//转字符
String(163)  // "163"
String(null) // "null"

// \转义
"micro\"major"  // "micro"major"
"micro\\major"  // "micro\major"
"micro\tmajor"  // "micro	major"

一些正则相关：

var str = 'aaa111bb22c3';
var rex = /[a-z]+([0-9]{3})/;

//字符串匹配正则表达式
str.match(rex);
//rex最后不带g,只获取第一个匹配的，且会把字符串中匹配正则表达式中括号内的部分也放到数组中。
// -->['aaa111', '111'];
//带g -->['aaa111'];

//测试字符串能否匹配表达式
rex.test(str);// --> true

//替换
str.replace(rex,'$1');// --> '111bb22c3'

 数组操作：

//arr.indexOf();
var telephones = [110,120,114];
telephones.indexOf(120);  // 1
telephones.indexOf(119);  // -1

//arr.forEach(function(item,index,array));
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var editScore = function(item,index,array){
	item.score += 5;
};
students.forEach(editScore);

//arr.reverse();
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.reverse();
students[0].score;  // 70

//arr.sort(function(a,b));
// function(a,b)会返回一个值，如果是小于0的值，就会将a所对应的元素排在前面。
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var byScore = function(a,b){
	return b.score-a.score;
};
students.sort(byScore);

//arr.sort();
var studentNames = ["wq","xl","gp"];
studentNames.sort();
studentNames;  // ["gp","wq","xl"]

//arr.push();插到最后一个。
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.push({id:4,score:90});

var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.push({id:4,score:90},{id:5,score:60});

//arr.unshift;插到第一个。
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.unshift({id:4,score:90});

//arr.shift();移除第一个并返回移除的值。
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.shift();  // {id:1,score:80}

//arr.pop();移除最后一个并返回移除的值。
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.pop();  // {id:3,score:70}

//arr.splice(移除的元素的索引号，移除的个数，插入的新元素);
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.splice(1,1,{id:4,score:90});

var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.splice(1,1);

var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
students.splice(1,0,{id:4,score:90});

//arr.slice();
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var newStudents = students.slice(0,2);

var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var newStudents = students.slice(0);

//arr.contat();
var students1 = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var students2 = [
	{id:4,score:90},
	{id:5,score:60}
];
var students3 = [
	{id:6,score:40},
	{id:7,score:30}
];
var newStudents = students1.concat(students2,students3);

//arr.join();
var emails = ["wq@163.com","gp@163.com","xl@163.com"];
emails.join(";");  // "wq@163.com;gp@163.com;xl@163.com"

//arr.forEach();
var scores = [60,70,80,90];
var newScores = [];
var addScore = function(item,index,array){
	newScores.push(item+5);
};
scores.forEach(addScore);
newScores; // [65,75,85,95]
console.log(scores.forEach(addScore));
console.log(scores);

//arr.map(); 有返回值
var scores = [60,70,80,90];
var addScore = function(item,index,array){
	return item+5;
};
scores.map(addScore);  // [65,75,85,95]

// arr.reduce(function(previousResult,item,index,array),previousResult的初始值);
var students = [
	{id:1,score:80},
	{id:2,score:50},
	{id:3,score:70}
];
var sum = function(previousResult,item,index,array){
	console.log(previousResult);
	console.log(item);
	return previousResult+item.score;
};
students.reduce(sum,0);  // 200