模拟京东按键输入内容，快递单号查询案例

代码样式展示

var input = document.querySelector('input');
var b = document.querySelector('.b');
document.body.addEventListener('keyup', function (e) {
    if (e.keyCode === 'S'.charCodeAt(0)) {
        input.focus();  // 获取焦点
    }
})

// 禁止按下s后的将s输入到文本框中
input.addEventListener('keyup', function (e) {
    e.stopPropagation();
}, true)

input.addEventListener('keyup', function (e) {
    e.stopPropagation();
    b.innerText = a.target.value;
}, true)

// 有焦点时执行的操作
input.addEventListener('focus', function (a) {
    b.style.display = 'block';
})
// 失去焦点时执行的操作
input.addEventListener('blur', function (a) {
    b.style.display = 'none';
})

.clearfix:before,
.clearfix:after {
    content: "";
    display: table;
}

.clearfix:after {
    clear: both;
}

.clearfix {
    *zoom: 1;
}

li {
    list-style: none;
}

a {
    color: black;
    text-decoration: none;
}

* {
    margin: 0;
    padding: 0;
}

.w {
    position: relative;
    margin: 100px;

}

/*  */
.b {
    display: none;
    position: absolute;
    top: -40px;
    width: 171px;
    border: 1px solid rgba(0, 0, 0, .2);
    box-shadow: 0 2px 4px rgba(0, 0, 0, .2);
    padding: 5px 0;
    font-size: 18px;
    line-height: 20px;
    color: #333;
}

.b::before {
    content: '';
    width: 0;
    height: 0;
    position: absolute;
    top: 28px;
    left: 18px;
    border: 8px solid;
    border-style: solid dashed dashed;
    border-color: #fff transparent transparent;
}