2 js的20/80关键知识

1.

2

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;
}

　　

• shift+enter 换行

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

　　

3

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

　　

4

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

　　

5.

https://developer.mozilla.org/zh-CN/docs/Web/Reference/API

6

var b=document.querySelector("body")
undefined

b.setAttribute("style","background-color: black");
undefined

　　

var dark = "background-color: black; color: white;";
var day = "background-color: white; color: black;";

// var theme = {
//   dark : "background-color:black; color:white; ",
//   light : "background-color:white; color:black; "
// };

var button = document.querySelector(".nav");
var web = document.querySelector("body");

function lightSwitch() {
  if (web.style.cssText == dark){
      web.style.cssText = day;
      alert("Light Day");
  } else {
      web.style.cssText = dark;
      alert("Dark Day");
  }
}

button.onclick = lightSwitch