Deep dive into the basics of JavaScript
This time I will bring you in-depth JavaScript basic applications, What are the precautions for using JavaScript basic applications, the following are practical cases, let’s take a look take a look.
Function return value
Return value 1
<script>function show(){ return 'advb';
}var a=show();
alert(a); // 结果: advb</script>Return value 2
<script>function show(a, b){ return a+b;
}
alert(show(3, 5));</script>Return value 3
<script>function show(a, b){ //return; //没有return}
alert(show(3, 5)); //结果 : undefined</script>
<script>function show(a, b){ return; //没有return任何东西}
alert(show(3, 5)); //结果 : undefined</script>General summation
<script>function sum(a, b){ return a+b;
}
alert(sum(12, 6));</script>Sum of multiple parameters (arguments is a variable array)
<script>
function sum() { //arguments 是一个可变数组
var result=0; for(var i=0;i<arguments.length;i++)
{
result+=arguments[i];
} return result;
}
alert(sum(12, 6, 8, 6, 8, 6, 8)); //结果 : 54</script>```- CSS function gets properties when two parameters are passed in, and changes when three parameters are passed in Style
<html>
<head>
<meta charset="utf-8">
<title>CSS函数</title>
<script>
function css(obj, name, value)
{
if(arguments.length==2) //获取
{
return obj.style[name];
}
else
{
obj.style[name]=value; //修改
}
}
window.onload=function ()
{
var oDiv=document.getElementById('div1');
//alert(css(oDiv, 'width')); //获取到宽度 200px
css(oDiv, 'background', 'green'); //修改背景颜色为绿色
};
</script>
</head>
<body>
<div id="div1" style="width:200px; height:200px; background:red;">
</div>
</body>
</html>function getStyle(obj, name)
{if(obj.currentStyle) //由于currentStyle只兼容IE,所以在IE浏览器中他是true,其他浏览器中为false
{
return obj.currentStyle[name]; //IE
}
else
{ //计算样式 其中getComputedStyle(oDiv, xxx) 第二个参数可以随便填,一般习惯写false
return getComputedStyle(obj, false)[name]; //Chrome、FF
}
}Sample code:
Use the above function to obtain the non-interline style `backgroundColor`
window.onload=function (){var oDiv=document.getElementById('div1');
alert(getStyle(oDiv, 'backgroundColor'));
};
NoteThis function only Applicable to single style, composite style is not applicable!!!
Single style: width, height, position, etc.
Composite style: background, border, etc.
>
3. Array - Array basics
- Array usage
var arr=[12, 5, 8, 9]; //一般用这种创建方式,简单 var arr=new Array(12, 5, 8, 9); //也可以这样创建
- Array The attribute
can both be obtained and set: ①. You can get the number of arrays, ②. You can also use array.length = 1; to set the number of arrays;
Principles for using arrays: Only one type of variables should be stored in the array
Add
push(element), add an element from the tail
unshift(element), add an element from the head
shift(), delete an element from the head
- insert and delete `splice` (`phonetic symbol:[splaɪs]`): universal of arrays Operation
splice(start, length) //First parameter: Specify the position; Second parameter: Specify the length
splice(start, 0, element...)
Delete first, then insert
Delete first, then insert, which can be used as replacement
-Array connection (merge two arrays):concatconcat(array 2)
<script> var a = [1,2,3]; var b = [4,5,6]; alert(a.concat(b)); 结果:[1,2,3,4,5,6]; alert(b.concat(a)); 结果:[4,5,6,1,2,3]; </script>
- join(separator)Use the delimiter to combine array elements to generate a string (when learning ajax, use it to connect the URL)
<script> var arr = [1,2,3,4]; alert(arr.join('-')) //1-2-3-4 alert(arr.join('- -p')) //1- -p2- -p3- -p4 </script>
howmany Optional. This parameter specifies the maximum length of the returned array. If this parameter is set, no more substrings will be returned than the array specified by this parameter. If this parameter is not set, the entire string will be split regardless of its length.
"hello".split("") //可返回 ["h", "e", "l", "l", "o"]If you only need to return a part of characters, please use howmany parameters:
"hello".split("", 3) //可返回 ["h", "e", "l"]- Sort sort`sort([Comparison function])`, sort an array
Sort a string array
Sort a numeric array ① Sort a string array
<script> var arr=['float', 'width', 'alpha', 'zoom', 'left']; arr.sort(); alert(arr); //结果 ['alpha','float','left','width','zoom'] </script>
<script> var arr=[12, 8, 99, 19, 112]; arr.sort(); alert(arr); //结果: [112,12,19,8,99] //其实他把数字当成字符串来排序了 </script>
<script>
var arr=[12, 8, 99, 19, 112];
arr.sort(function (n1, n2){
if(n1<n2)
{
return -1;//只要是个负数就可以 -2,-7等都可以
}
else if(n1>n2)
{
return 1; //只要是个正数就够了
}
else
{
return 0;
}
});
alert(arr); //结果:[8,12,19,99,112]
</script> related articles! Recommended reading: The above is the detailed content of Deep dive into the basics of JavaScript. For more information, please follow other related articles on the PHP Chinese website!<script>var arr=[12, 8, 99, 19, 112];
arr.sort(function (n1, n2){ return n1-n2; //若果n1>n2,为正;如果n1<n2,为负;如果相等,则为0;});alert(arr);//结果:[8,12,19,99,112]
</script>
Background-related attributes in HTML and CSS
8 basic knowledge that must be paid attention to in JS
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