2 js的20/80关键知识

var a = 1;
undefined
a
1
alert(a);
undefined

var b = true;
var c = "Hi";
undefined
alert(b);
alert(c);
undefined

function foo(bar){
	alert(bar);
	return bar;
}
undefined
var z = foo("Hi");
undefined
z
"Hi"

function foo(bar)
{
	alert(bar);
	return bar;
}

function foo(bar){
	if (bar > 3){
		alert(bar + 1);
	} else {
		alert("Not enough");
	}
}
undefined
foo(5)
undefined
foo(2);
undefined

var arr = []
undefined

function foo(bar){
	if (bar > 3){
		arr.push(bar);
	} else {
		alert("Not enough");
		}
}
undefined

foo(2);
undefined

foo(6);
undefined
arr;
[6]

var o = {
	one:1,
	two:2
}
undefined
o.one
1
o.two
2

document
#document

document.querySelector("#sidebar")
<div id=?"sidebar">?…?</div>?

var el = document.querySelector("#sidebar");
undefined

el
<div id=?"sidebar">?…?</div>?

el.setAttribute("style","display:none;")
undefined