javascript中关于类型判断的一些疑惑小结

let a = undefined;
typeof a
"undefined"

let b = false;
typeof b
"boolean"

let c = 12;
typeof c
"number"

let d = '12';
typeof d
"string"

let f = function () {};
typeof f
"function"

let str = new String('abc');
typeof str
" "

let num = new Number(12);
typeof num
" "

var func = new Function();
typeof func; 
"function"

typeof null
" "

let arr = [1, 2, 3];
typeof arr
" "

arr instanceof Array //true

Array.isArray(arr) // true

arr.constructor.name // "Array"

var   = document.createElement(' ');
document.body.appendChild( );
xArray = window. s[window. s.length-1].Array;
var arr = new xArray(1,2,3); // [1,2,3]

// Correctly checking for Array
Array.isArray(arr); // true
// Considered harmful, because doesn't work though  s
arr instanceof Array; // false

arr.constructor.name //"Array"

isNaN(1/'a') // true

let nan1 = NaN
let nan2 = NaN
 .is(nan1, nan2)
true