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@jherax
Last active April 13, 2016 18:06
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JavaScript coercion
VALOR COERCIÓN
------- ---------
false false
0 false
“” false
NaN false
null false
undefined false
(function (u) { //u = undefined
var fn = function() {},
o = { valueOf: function() { return 7 } };
//coerción en diferentes tipos de objetos
write("a.", fn); //!!bool: true, type: function
write("b.", fn()); //!!bool: false, type: undefined
write("c.", u); //!!bool: false, type: undefined
write("d.", 0); //!!bool: false, type: number
write("e.", ""); //!!bool: false, type: string
write("f.", +""); //!!bool: false, type: number
write("g.", +"x"); //!!bool: false, type: number (NaN)
write("h.", null); //!!bool: false, type: object [Null]
write("i.", []); //!!bool: true, type: object [Array]
write("j.", {}); //!!bool: true, type: object [Object]
write("k.", o); //!!bool: true, type: object [Object]
write("l.", +o); //!!bool: true, type: number
function padRight (val, len) {
var c = " ";
len = len || 10;
return (val + new Array(len).join(c)).slice(0, len);
}
function write (nom, val) {
console.log(nom, "type:", padRight(typeof val),
"!!bool:", padRight(!!val, 7), "value:", val);
}
}());
(function () {
//accediendo elementos del array
var array = ["cero", "uno", "dos"];
console.log("a.", array[+[]]); //coerción a number
console.log("b.", array[+!![]]); //coerción a number
console.log("c.", array['1']); //coerción a number
console.log("d.", array[ 2 ]);
//accediendo propiedades de un objeto
var obj = { id: 1, "5": "cinco" };
console.log("e.", obj["5"]); //propiedad de obj
console.log("f.", obj[ 5 ]); //coerción a string
//coerción con números y strings
console.log("g.", 5 - '3'); // -> 2
console.log("h.", 5 + '3'); // -> "53"
console.log("i.", 5 + (+'3')); // -> 8
console.log("j.", 5 * '3'); // -> 15
console.log("k.", "" - 3); // -> -3
console.log("l.", true + 1); // -> 2
console.log("m.", '1' + true); // -> 1true
console.log("n.", '1' - true); // -> 0
console.log("o.", false - true); // -> -1
//coerción con fechas
var d = new Date();
console.log("p.", +d); //number, llama a .valueOf()
console.log("q.", d + ""); //string, llama a .toString()
}());
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jherax commented Jun 3, 2015

Tomado del artículo: Coerción en JavaScript

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