When I was looking at the JavaScript Template source code, I found a very interesting usage for generating functions. I thought, isn’t this metaprogramming?
JavaScript Metaprogramming
Metaprogramming refers to the writing of certain types of computer programs that write or manipulate other programs (or themselves) as their data, or complete some work at runtime that should be completed at compile time.
JavaScript eval
The eval() function evaluates a string and executes the JavaScript code within it.
It can be used as follows:
eval("x=10;y=20;document.write(x*y)")
Of course, this is only used to execute a certain function, but this product is very cost-effective and error-prone.
The eval function should be avoided whenever possible.
So a better way is to use New Function()
The big difference between using New Function() and eval() is that eval is not just a function,
eval() evaluates a string as a JavaScript expression within the current execution scope and can access local variables. New Function() parses a string stored in it into a function object that can then be called by JavaScript code. Because the code runs in a separate scope, local variables cannot be accessed.
In other words, eval() will interfere with the scope of the current function. .
JavaScript new Function()
The Function constructor creates a new Function object. In JavaScript, each function (function) is actually a Function object. The Function object generated using the Function constructor is parsed when the function is created. This is less efficient than if you declare a function and call it in your code, because functions declared using function statements are parsed along with other statements.
New Function() will be less efficient in comparison, and this is what we can predict under the current situation.
A simple example looks like this:
var add = new Function(['x', 'y'], 'return x y');
new Function() will parse the string into a function. . Then we can execute it through apply
Function.apply(null, args)
And this is what I see in the JavaScript Template:
new Function(
tmpl.arg ',tmpl',
"var _e=tmpl.encode" tmpl.helper ",_s='"
str.replace(tmpl.regexp, tmpl.func)
"';return _s;"
);
Of course we have other methods.

去掉重复并排序的方法:1、使用“Array.from(new Set(arr))”或者“[…new Set(arr)]”语句,去掉数组中的重复元素,返回去重后的新数组;2、利用sort()对去重数组进行排序,语法“去重数组.sort()”。

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方法:1、利用“点击元素对象.unbind("click");”方法,该方法可以移除被选元素的事件处理程序;2、利用“点击元素对象.off("click");”方法,该方法可以移除通过on()方法添加的事件处理程序。

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foreach不是es6的方法。foreach是es3中一个遍历数组的方法,可以调用数组的每个元素,并将元素传给回调函数进行处理,语法“array.forEach(function(当前元素,索引,数组){...})”;该方法不处理空数组。


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