If I add these value on a Map:
var m = new Map();
m.set(1, "black");
m.set(2, "red");
m.set("colors", 2);
m.set({x:1}, 3);
m.forEach(function (item, key, mapObj) {
document.write(item.toString() + "<br />");
});
document.write("<br />");
document.write(m.get(2));
document.write("<br />");
document.write(m.get({x:1}));
This prints:
black
red
2
3
red
undefined
Why I get undefined
in the last line? And is there a way to retrieve the value of a object key stored in a Map?
You will probably need a reference to the object:
var m = new Map();
var o = {x:1};
m.set(o, 3);
m.get(o); //3
You need the object reference for getting the object. Any new literal is a new object, and is different.
var obj = { x: 1 }, m = new Map(); m.set(1, "black"); m.set(2, "red"); m.set("colors", 2); m.set(obj, 3); m.forEach(function (item, key, mapObj) { console.log(item.toString()); }); console.log(m.get(2)); console.log(m.get(obj)); console.log([...m]);
you have undefined simply because
document.write(m.get({x:1}));
the object you are fetching at this line is not the same as the one here
m.set({x:1}, 3);
try this:
var m = new Map();
var obj = {x:1};
m.set(1, "black");
m.set(2, "red");
m.set("colors", 2);
m.set(obj, 3);
m.forEach(function (item, key, mapObj) {
document.write(item.toString() + "<br />");
});
document.write("<br />");
document.write(m.get(2));
document.write("<br />");
document.write(m.get(obj));
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