JS九

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定时器

点击倒计时

html

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<div class="box">
    <input type="text"/>
    <button>点击发送短信</button>
</div>

script

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window.onload = function(){
    var btn = document.getElementsByTagName("button")[0];
    var count = 5;          //多少秒倒计时
    var timer = null;        // 定时器的名字
    btn.onclick = function(){
        clearInterval(timer);     // 先清除掉原来的定时器
        this.disabled = true;     // this 指向的是 btn
        var that = this;           // 把 btn 对象 给 that
        timer = setInterval(send,1000);
        function send(){
          //            alert(this); // this 指向的是 定时器  window
          //            alert(that);
            count--;
            if(count >= 0){
               that.innerHTML = '还有'+ count + "秒";
            }
            else {
                that.innerHTML = "重新发送短信";
                that.disabled = false;
                clearInterval(timer);      // 清除定时器
                count = 5;
            }
        }
    }
}

页面多少秒后跳转

html

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<div id="demo"></div>

script

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var demo = document.getElementById("demo");
var count = 5;
setInterval(fn,1000);
function fn(){
    count--;
    demo.innerHTML = "页面将在" +  count + "后跳转";
    if(count <= 0){
        window.location.href = "http://www.baidu.com";
    }
}

转换为字符串

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var txt = 12345;
console.log(typeof (txt + ""));       //string
console.log(typeof String(txt));      //string
console.log(typeof txt.toString());   //string

字符串常见操作方法

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var txt1 = "abcdefg"
var txt2 = "123456";
var txt3 = "一二三四五六"
var txt4 = " 123456 "
//返回指定索引位置的字符
console.log(txt1.charAt(3));        //d
console.log(txt2.charAt(3));        //4
console.log(txt3.charAt(3));        //四
//提取字符串的片断，并在新的字符串中返回被提取的部分
console.log(txt1.slice(1,4));       //bcd
console.log(txt2.slice(1,4));       //234
console.log(txt3.slice(1,4));       //二三四
//移除字符串首尾空白
console.log(txt4.trim());