前端基础笔记

【javascript】引用类型-基本包装类型

2017-11-13  本文已影响2人  shanruopeng 
var s1 = "some text";
var s2 = s1.substring(2);

var s1 = "some text";
s1.color = "red";
alert(s1.color); //undefined

var s1 = new String("some text");
s1.name = "sss";
console.log(s1.name);//sss

var obj = new Object("some text");
alert(obj instanceof String); //true

var value = "25";
var number = Number(value); //转型函数
alert(typeof number); //"number"
var obj = new Number(value); //构造函数
alert(typeof obj); //"object"

Boolean 类型

var booleanObject = new Boolean(true);

var falseObject = new Boolean(false);
var result = falseObject && true;
alert(result); //true

var falseValue = false;
result = falseValue && true;
alert(result); //false

alert(typeof falseObject); //object
alert(typeof falseValue); //boolean
alert(falseObject instanceof Boolean); //true
alert(falseValue instanceof Boolean); //false

Number 类型

var numberObject = new Number(10);

var num = 10;s
alert(num.toString()); //"10"
alert(num.toString(2)); //"1010"
alert(num.toString(8)); //"12"
alert(num.toString(10)); //"10"
alert(num.toString(16)); //"a"

var num = 10;
alert(num.toFixed(2)); //"10.00"

var num = 10.005;
alert(num.toFixed(2)); //"10.01"

var num = 10;
alert(num.toExponential(1)); //"1.0e+1"

var num = 99;
alert(num.toPrecision(1)); //"1e+2"
alert(num.toPrecision(2)); //"99"
aler t(num.toPrecision(3)); //"99.0"

var numberObject = new Number(10);
var numberValue = 10;
alert(typeof numberObject); //"object"
alert(typeof numberValue); //"number"
alert(numberObject instanceof Number); //true
aler t(numberValue instanceof Number); //false

String类型

var stringObject = new String("hello world");
var stringValue = "hello world";
alert(stringValue.length); //"11"

1、字符方法 charAt()、charCodeAt()

var stringValue = "hello world";
alert(stringValue.charAt(1)); //"e"

var stringValue = "hello world";
alert(stringValue.charCodeAt(1)); //输出"101"

var stringValue = "hello world";
alert(stringValue[1]); //"e"

2、字符串操作方法 concat()、slice()、substr()和substring()

var stringValue = "hello ";
var result = stringValue.concat("world");
alert(result); //"hello world"
alert(stringValue); //"hello"

var stringValue = "hello ";
var result = stringValue.concat("world", "!");
alert(result); //"hello world!"
alert(stringValue); //"hello"

var stringValue = "hello world";
alert(stringValue.slice(3)); //"lo world"
alert(stringValue.substring(3)); //"lo world"
alert(stringValue.substr(3)); //"lo world"
alert(stringValue.slice(3, 7)); //"lo w"
alert(stringValue.substring(3,7)); //"lo w"
alert(stringValue.substr(3, 7)); //"lo worl"

var stringValue = "hello world";
alert(stringValue.slice(-3)); //"rld"
alert(stringValue.substring(-3)); //"hello world"
alert(stringValue.substr(-3)); //"rld"
alert(stringValue.slice(3, -4)); //"lo w"
alert(stringValue.substring(3, -4)); //"hel"
alert(stringValue.substr(3, -4)); //""（空字符串）

3、字符串位置方法: indexOf()和lastIndexOf()

var stringValue = "hello world";
alert(stringValue.indexOf("o")); //4
alert(stringValue.lastIndexOf("o")); //7

var stringValue = "hello world";
alert(stringValue.indexOf("o", 6)); //7
alert(stringValue.lastIndexOf("o", 6)); //4

var stringValue = "Lorem ipsum dolor sit amet, consectetur adipisicing elit";
var positions = new Array();
var pos = stringValue.indexOf("e");
while(pos > -1){
    positions.push(pos);
    pos = stringValue.indexOf("e", pos + 1);
}
alert(positions); //"3,24,32,35,52"

4、trim()方法

var stringValue = " hello world ";
var trimmedStringValue = stringValue.trim();
alert(stringValue); //" hello world "
alert(trimmedStringValue); //"hello world"

5、字符串大小写转换方法
toLowerCase()、toLocaleLowerCase()、toUpperCase()和toLocaleUpperCase()

var stringValue = "hello world";
alert(stringValue.toLocaleUpperCase()); //"HELLO WORLD"
alert(stringValue.toUpperCase()); //"HELLO WORLD"
alert(stringValue.toLocaleLowerCase()); //"hello world"
alert(stringValue.toLowerCase()); //"hello world"

6、字符串的模式匹配方法: match()、search()、replace()和split()

var text = "cat, bat, sat, fat";
var pattern = /.at/;
//与pattern.exec(text)相同
var matches = text.match(pattern);
alert(matches.index); //0
alert(matches[0]); //"cat"
alert(pattern.lastIndex); //0

var text = "cat, bat, sat, fat";
var pos = text.search(/at/);
aler t(pos); //1

var text = "cat, bat, sat, fat";
var result = text.replace("at", "ond");
alert(result); //"cond, bat, sat, fat"
result = text.replace(/at/g, "ond");
aler t(result); //"cond, bond, sond, fond"
字符序列 替换文本
$$ $
$& 匹配整个模式的子字符串。与RegExp.lastMatch的值相同
$' 匹配的子字符串之前的子字符串。与RegExp.leftContext的值相同
$` 匹配的子字符串之后的子字符串。与RegExp.rightContext的值相同
$n 匹配第n个捕获组的子字符串，其中n等于0～9。例如，$1是匹配第一个捕获组的子字符串，$2是匹配第二个捕获组的子字符串，以此类推。如果正则表达式中没有定义捕获组，则使用空字符串
$nn 匹配第nn个捕获组的子字符串，其中nn等于01～99。例如，$01是匹配第一个捕获组的子字符串，$02是匹配第二个捕获组的子字符串，以此类推。如果正则表达式中没有定义捕获组，则使用空字符串 
var text = "cat, bat, sat, fat";
result = text.replace(/(.at)/g, "word ($1)");
alert(result); //word (cat), word (bat), word (sat), word (fat)

function htmlEscape(text){
    return text.replace(/[<>"&]/g, function(match, pos, originalText){
        switch(match){
            case "<":
                return "&lt;";
            case ">":
                return "&gt;";
            case "&":
                return "&amp;";
            case "\"":
                return "&quot;";
            }
    });
}
alert(htmlEscape("<p class=\"greeting\">Hello world!</p>"));
//&lt;p class=&quot;greeting&quot;&gt;Hello world!&lt;/p&gt;

var colorText = "red,blue,green,yellow";
var colors1 = colorText.split(","); //["red", "blue", "green", "yellow"]
var colors2 = colorText.split(",", 2); //["red", "blue"]
var colors3 = colorText.split(/[^\,]+/); //["", ",", ",", ",", ""]

7、localeCompare()方法

var stringValue = "yellow";
alert(stringValue.localeCompare("brick")); //1
alert(stringValue.localeCompare("yellow")); //0
alert(stringValue.localeCompare("zoo")); //-1

function determineOrder(value) {
    var result = stringValue.localeCompare(value);
    if (result < 0){
        alert("The string 'yellow' comes before the string '" + value + "'.");
    } else if (result > 0) {
        alert("The string 'yellow' comes after the string '" + value + "'.");
    } else {
        alert("The string 'yellow' is equal to the string '" + value + "'.");
    }
}
determineOrder("brick");
determineOrder("yellow");
determineOrder("zoo");

8、fromCharCode()方法

alert(String.fromCharCode(104, 101, 108, 108, 111)); //"hello"
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