2 JS of 20/80 key knowledge

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var a = 1;undefineda1alert (a); undefined

　　

var b = True;var c = "Hi"; Undefinedalert (b); alert (c); undefined

　　

function foo (bar) {alert (bar); return bar;} Undefinedvar z = foo ("Hi"); Undefinedz "HI"

　　

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

　　

• Shift+enter line break

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

　　

3

var arr = []undefinedfunction foo (bar) {if (Bar > 3) {arr.push (bar);} else {alert ("Not Enough");}} Undefinedfoo (2); Undefinedfoo (6); Undefinedarr; [6]

　　

var o = {One:1,two:2}undefinedo.one1o.two2

　　

4

Document#documentdocument.queryselector ("#sidebar") <div id=? " Sidebar ">?...? </div>?var el = document.queryselector ("#sidebar"); Undefinedel<div id=? " Sidebar ">?...? </div>?el.setattribute ("Style", "display:none;") Undefined

　　

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2 JS of 20/80 key knowledge