1. Use clever judgment:
In js, NaN, undefined,Null,0,"" is false when converted to bool, so it can be written like this.
if(!obj) {}
It indicates what an object does if false, because if obj is any of the above, then it is false, !false is true, so there is no need if(obj==null || obj == NaN ......).
2. Use operators skillfully:
There is a very classic trick to get the timestamp.
var dataspan = new Date()*1;
We know that js is a weak-type language. Date() will return a string representing time. Using this string for arithmetic operation will get the conversion, which is the time stamp of the result.
3. Use regular expressions skillfully:
/.a/('xsas')
//It is equivalent to creating a reg object and calling the exec method. Of course, other methods can also be called, such as: test(), match(), etc.
4. Take the maximum and minimum values of the array:
var values = [1,2,3,40,23];
var max = (Math,values);
Call, set the object to Math, and then pass a Values to determine the maximum value.
5. Memory optimization:
function p(){='moersing'}; var p1 = new p();
.......
p1=null; //After executing the operation, finally manually dereference to p1.
6. The most popular way to create objects (prototype mode):
function c(){
='moersing';
=18;
=['javascript develop','C# develop'];
}
={
displayBookName:function (){
foreach(var t in )
{
([t]);
}
}
}
The biggest disadvantage of the prototype construction pattern is the sharing of reference types, so, define the reference type in the constructor, and define the general method in the prototype, and use this reference.
7. Block-level scope and private variables
In javascript, there is no such thing as block-level scope and private variables, but using some features can imitate these effects.
7.1 block-level scope:
(function(){
//Block level scope
}
)();
Add a bracket outside an anonymous function, and I call it "function standardization", that is, it can be called like a standard function, such as:
var name =function(){};
(name)();//This is not written in general;
The advantage of doing this is that the variables in the function cannot be accessed outside () and become a block-level scope. This method is generally used when writing plug-ins, and no additional variables are added globally. Moreover, after the function is executed, the variables defined internally are destroyed, so there will be no problems with the closure feature.
7.2 Private variables:
function private()
{
var name = 'moersing';
= function(){
return ;
}
}
Private variables are actually using the scope of the function as a limit (inaccessible externally), and then defining a method, which returns the corresponding variable, and that's all.
NodeList:
nodeList is a dynamic element, which means that if any element is added to the document, nodeList will be updated in real time, such as:
var alldiv = ('div');
for(var i=0;i<;i++)
{
var div = ('div');
= ();
(div);
}
This code will create an infinite loop. A div is created in the loop, and then the appendChild method will add it to the body. Then, all alldivs will be updated immediately. Therefore, i< will never be valid. To solve this problem, you can use the following method:
var alldiv = ('div');
var len,i;
for(i=0,len=;i<len;i++)
{
var div = ('div');
= ();
(div);
}
Here is a suggestion: it is best not to frequently operate on NodeList, because each operation will perform a query of the DOM tree.
In addition to the methods introduced above, the newly added API of HTML5 (selector API Level1) can also solve this problem. It is similar to C#'s timely query. As for what is linq timely query, I will update the blog in the future. Please pay attention:
var allDiv= ('div');
for(var i=0;i<;i++)
{
var div = ('div');
= ();
(div);
}
querySelectorAll requires a parameter, a CSS selector, similar to $() in jquery, and the NodeList it returns is a timely, non-dynamic DOM collection.
There is also a querySelector that returns the first element that matches. For details about HTML5 API, see
http:///standards/techs/dom#w3c_all
or
/zh-CN/docs/Web/API
In addition, I am also planning a blog that specializes in HTML5 API, please pay attention.
performance:
Don't do such stupid things (I've done it...)
for(var i=0;i<10;i++)
{
('ul').innerHTML="<li>"+i+"</li>";
}
Assigning values to the innerHTML of the object will call the built-in C++ parser to parse the string. Although it is very fast, it is best not to operate like this, as there will be certain performance loss.
It's best to do this:
var ih=null;
for(var i=0;i<10;i++)
{
ih+="<li>"+i+"</li>";
}
('ul').innerHTML=ih;
Some other performance optimization topics will be updated when you have time.
The above is the entire content of this article, I hope you like it.