Shulou(Shulou.com)06/01 Report--

This article mainly introduces the example analysis of the js function, which has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, let the editor take you to understand it.

Function 1 function default value func = (l, m = 3, n = 4) = > (l * m * n); func (2) / / output: 24

Note that the default parameter will be used when the input parameter is undefined or not, but the default parameter will still be overridden by passing in null.

2 forced parameters

By default, if you do not pass a value to a function parameter, JS sets the function parameter to undefined. Some other languages issue warnings or errors. To perform parameter assignment, you can use if statements to throw undefined errors, or you can use forced parameters.

Mandatory = () = > {throw new Error ('Missing parameterized');} foo = (bar = mandatory ()) = > {/ / if no parameter is passed here, the manadatory function will report an error return bar;} 3 implicit return value

The return value is the keyword that we usually use to return the final result of the function. The arrow function of only one statement can implicitly return the result (the function must omit the curly braces {} in order to omit the return keyword).

To return a multiline statement, such as object text, you need to wrap the function body with () instead of {}. This ensures that the code evaluates as a single statement.

Function calcCircumference (diameter) {return Math.PI * diameter} / / abbreviated as: calcCircumference = diameter = > (Math.PI * diameter;) 4 lazy load function

In a certain scenario, we have a judgment statement in our function, which usually does not change during the whole project run, so the judgment branch will only run a specific branch during the whole project running. then you can consider lazily loading the function.

Function foo () {if (a! = = b) {console.log ('aaa')} else {console.log (' bbb')} / / optimized function foo () {if (a! = b) {foo = function () {console.log ('aaa')}} else {foo = function () {console.log (' bbb')} return foo ();}

Then the method will be overridden after the first run, and the judgment will not be executed the next time it is run. Of course, there is only one judgment now, if there are many judgments and the branches are more complex, then the savings in resources are still considerable.

5 one-time function

In the same way as the lazy load function above, you can overwrite the current function in the function body, then you can create an one-time function, and the code before re-assignment is equivalent to running only once, which is suitable for running initialization code that only needs to be executed once.

Var sca = function () {console.log ('msg') sca = function () {console.log (' foo')}} sca () / / msgsca () / / foosca () / / foo Thank you for reading this article carefully. I hope the article "sample Analysis of js function" shared by the editor will be helpful to you. At the same time, I also hope you will support us, pay attention to the industry information channel, and more related knowledge is waiting for you to learn!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.