Ola amigos!
JavaScript idiosyncrasies
Do you know js ?
before answers to the question please read more than 20 books about js technology and only then answer
please copy this project and share with friends :)
¯\_(ツ)_/¯
https://odykyi.github.io/javascript-idiosyncrasies/
https://github.com/odykyi/javascript-idiosyncrasies
This is a collection of things in JavaScript that may not be well recognized, especially to beginners.
Disclaimer: Some of these snippets are simply to demonstrate the quirky parts of JavaScript and by no means encourage best practices and should never be seen in production code.
Q. What’s the result?
(function() {
return `text 'inner'` == `text "inner"`;
})();
A.
false
Q. What’s the result?
(function() {
var obj = {
valueOf: function(){
return 3;
},
toString: function(){
return 2;
},
}
return obj + 4;
})();
A.
7
Q. What’s the result?
(function() {
var foo = new Object();
var bar = new Object();
var map = new Object();
map[foo] = 'foo';
map[bar] = 'bar';
return map[foo];
})();
A.
"bar"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return NaN === NaN;
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
function foo() {
return 'a';
}
return foo();
function foo() {
return 'b';
}
})();
A.
"b"
| JSBin | JSBin explained |
Q. What’s the result?
(function(limit) {
for (var i = 0; i < limit; i++) {
setTimeout(function() {
console.log(i);
}, 0);
}
})(3);
A.
3
3
3
| JSBin | JSBin explained |
Q. What’s the result?
(function(a, b) {
arguments[1] = 3;
return b;
})(1, 2);
A.
3
| JSBin | JSBin explained |
Q. What’s the result?
(function(a, b, c) {
delete arguments[0];
return arguments.length;
})(1, 2, 3);
A.
3
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (function (a, b) {}).length;
})();
A.
2
| JSBin | JSBin explained |
Q. What’s the result?
(function(a, b) {
var foo, bar;
foo = (bar = a, b);
return foo;
})(1, 2);
A.
2
| JSBin | JSBin explained |
Q. What’s the result?
(function(undefined) {
var foo;
return foo === undefined;
})(true);
A.
false
| JSBin | JSBin |
Q. What’s the result?
(function(n) {
return ~(n);
})(-3);
A.
2
| JSBin | JSBin explained |
Q. What’s the result?
(function(n) {
return ~~n;
})(-1.5);
A.
-1
| JSBin | JSBin explained |
Q. What’s the result?
(function(x) {
return !!x;
})('a');
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return typeof null === 'null';
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return +(new Date())
})();
A.
1393812837139
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (new Date()).valueOf();
})();
A.
1393812845834
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return ''+(new Date());
})();
A.
"Sun Mar 02 2014 18:14:01 GMT-0800 (PST)"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var foo = 'a';
(function(foo) {
foo = 'b';
})(foo);
return foo;
})();
A.
"a"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return arguments.toString();
})();
A.
"[object Arguments]"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (function(){}) === (function(){});
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function(n) {
return n === new Number(n);
})(10);
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function(x) {
return new String(x) === x;
})('a');
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return [1+1] === [2];
})()
A.
false
| JSbin | JSBin explained |
Q. What’s the result?
(function() {
return {foo: 'bar'} === {foo: 'bar'};
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
for(;;);
return 1;
})();
A.
*Infinite loop*
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return ['10','10','10','10'].map(parseInt);
})();
A.
[10, NaN, 2, 3]
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var o = {
toString: function() {
return 'a';
},
valueOf: function () {
return 1;
}
};
return o + o;
})();
A.
2
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var f = function g() {
return 1;
};
return g();
})();
A.
ReferenceError: g is not defined
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return void (1+1);
})();
A.
undefined
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var a = [1,2];
var b = a;
a = [1,2];
return a === b;
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var x = 1;
return (function () {
return x;
var x = 2;
})();
})();
A.
undefined
| JSBin | JSBin explained |
Q. What’s the result?
(function(n) {
var even = function (num) {
return (num === 0) || !(even(num - 1))
};
var _even = even;
even = void 0;
return _even(n);
})(2);
A.
TypeError: undefined is not a function
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var n;
function name() {
return this.name
};
n = name.bind({name: 'foo'});
n = n.bind({name: 'bar'})
return n();
})();
A.
"foo"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return ('3' > '12') === ('03' > '12');
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return Math.pow(2,53) === (Math.pow(2,53) + 1);
}();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return Math.pow(2,1024) === Infinity;
})();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (Infinity - 100) === Infinity;
}();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (0.1 + 0.2 === 0.3);
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (0.1).toFixed(20);
})();
A.
"0.10000000000000000555"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return parseFloat('3.3.4');
})();
A.
3.3
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return 010;
})();
A.
8
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return (parseInt('10000000000000000', 10) ===
parseInt('10000000000000001', 10)
);
})();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function(n) {
return (Function)('var n = n || 2; return n;')(n);
})(1);
A.
2
| JSBin | JSBin explained |
Q. What’s the result? (assuming window scope)
var a = 1;
b = 1;
(function() {
return (delete window.a) === (delete window.b);
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function(x) {
var isMatch,
regex = /[\w]/gi;
return (regex.test(x) === regex.test(x));
})('a');
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return ![];
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return +[];
})();
A.
0
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return [][[]];
})();
A.
undefined
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return +!+[];
})();
A.
1
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return []+[];
})();
A.
""
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return true + 1;
})();
A.
2
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return 1 / '';
})();
A.
Infinity
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return 1 * null;
})();
A.
0
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return new Array() == false;
})();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
if ([]) {
return [] == false;
}
})();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return ''.concat(null);
})();
A.
"null"
| JSBin | JSBin explained |
Q. What’s the result?
(function(a, b) {
return a + + b;
})('a','b');
A.
"aNaN"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
Object.prototype.foo = 'foo';
return foo;
})();
A.
"foo"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return 1000 === 1e3;
})();
A.
true
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return 9999999999999999;
})();
A.
10000000000000000
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
(function() {
var a = b = 1;
})();
return typeof a === typeof b;
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return Array(3).map(function(o) { return 'a'; });
})();
A.
[undefined, undefined, undefined]
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var foo = [0,1,2];
foo[10] = 10;
return foo.filter(function(n) { return n === undefined; });
})();
A.
[]
| JSBin | JSBin explained |
Q. What’s the result?
(function(x) {
var ret = null;
switch(x) {
case 'A':
ret = 'A';
break;
default:
ret = 'unknown';
break;
}
return ret;
})(new String('A'));
A.
"unknown"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
var x = {};
return x.prototype === Object.getPrototypeOf(x);
})();
A.
false
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
function foo() {}
foo.name = 'bar';
return foo.name;
})();
A.
"foo"
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
return Array(5).join(',').length;
})();
A.
4
| JSBin | JSBin explained |
Q. What’s the result?
(function(x) {
return x++ + ++x;
})(2);
A.
6
| JSBin | JSBin explained |
Q. What’s the result?
(function() {
'use strict';
let type = typeof foo;
let foo = 1;
return type;
})();
A.
ReferenceError: foo is not defined
License
Released under the MIT License.