I would like to create some custom JS syntax. Is there a way I can write a method so that the following would work:
var someDict = {"abc": 1, "efg": 2}
someDict.keys
someDict.values
instead of:
Object.keys(someDict)
Object.values(someDict)
In Swift this sort of thing can be done via extensions, I'm just wondering if there's a way in JS.
You can create an object with getters:
class ObjWithKeyValGetters {
constructor(obj) {
Object.assign(this, obj);
}
get keys() {
return Object.keys(this);
}
get values() {
return Object.values(this);
}
}
const myObj = new ObjWithKeyValGetters({"abc": 1, "efg": 2});
console.log(myObj.keys);
console.log(myObj.values);
Maybe you are looking for prototype . you can add new methods to Object with prototype like :
var current = Object.prototype.valueOf;
// Since my property "-prop-value" is cross-cutting and isn't always
// on the same prototype chain, I want to modify Object.prototype:
Object.prototype.valueOf = function() {
if (this.hasOwnProperty('-prop-value')) {
return this['-prop-value'];
} else {
// It doesn't look like one of my objects, so let's fall back on
// the default behavior by reproducing the current behavior as best we can.
// The apply behaves like "super" in some other languages.
// Even though valueOf() doesn't take arguments, some other hook may.
return current.apply(this, arguments);
}
}
as modified MDN pollyfill for Object.keys:
Object.prototype.pollufillKeys = (function() {
'use strict';
var hasOwnProperty = Object.prototype.hasOwnProperty,
hasDontEnumBug = !({
toString: null
}).propertyIsEnumerable('toString'),
dontEnums = [
'toString',
'toLocaleString',
'valueOf',
'hasOwnProperty',
'isPrototypeOf',
'propertyIsEnumerable',
'constructor'
],
dontEnumsLength = dontEnums.length;
return function(obj) {
if (typeof obj !== 'function' && (typeof obj !== 'object' || obj === null)) {
throw new TypeError('Object.keys called on non-object');
}
var result = [],
prop, i;
for (prop in obj) {
if (hasOwnProperty.call(obj, prop)) {
result.push(prop);
}
}
if (hasDontEnumBug) {
for (i = 0; i < dontEnumsLength; i++) {
if (hasOwnProperty.call(obj, dontEnums[i])) {
result.push(dontEnums[i]);
}
}
}
return result;
};
}());
