JS daily question (11)

js A daily topic

** hypothesis d It's within the scope of “ empty ” object ：
var d = {};
What is accomplished using the following code ？
[‘zebra’,‘horse’].forEach(function(k){
d[k] = undefined;
});
a
**
" answer ： The code snippet shown above is in the object d Two properties are set on the . Ideally , For javaScript Object is evaluated as undefined . But running this code marks these properties as objects “ Own attributes ”.

This is a useful strategy to ensure that objects have a set of defined properties . Pass the object to Object.keys Will return an array containing these set keys （ Even if their values are undefined ）.
"

The following code will be output to the console .

console.log((function f(n){
    
return ((n>1)? n*f(n-1) : n )
})(10))

**
This code will output 10 The value of the factorial （ namely 10！ or 3,628,800）.
Here's why ：
Name the function f（） Call itself recursively , Until it calls f(1), It simply returns 1. therefore , That's what it does ：
f(1):returns n ,which is 1
f(2):returns 2f(1) ,which is 2
f(3):returns 3f(2) ,which is 6
f(4):
.
.
.
**
Make a little progress every day ！！！！