I have to dynamically fetch the properties and functions of a ES6 class. Is this even possible?
Using a for...in loop, I only get to loop through the properties of a class instance:
class Foo {
constructor() {
this.bar = "hi";
}
someFunc() {
console.log(this.bar);
}
}
var foo = new Foo();
for (var idx in foo) {
console.log(idx);
}
Output:
bar
The members of a class are not enumerable. To get them, you have to use Object.getOwnPropertyNames:
var propertyNames = Object.getOwnPropertyNames(Object.getPrototypeOf(foo));
// or
var propertyNames = Object.getOwnPropertyNames(Foo.prototype);
Of course this won't get inherited methods. There is no method that can give you all of them. You'd have to traverse the prototype chain and get the properties for each prototype individually.
This function will get all functions. Inherited or not, enumerable or not. All functions are included.
function getAllFuncs(toCheck) {
const props = [];
let obj = toCheck;
do {
props.push(...Object.getOwnPropertyNames(obj));
} while (obj = Object.getPrototypeOf(obj));
return props.sort().filter((e, i, arr) => {
if (e!=arr[i+1] && typeof toCheck[e] == 'function') return true;
});
}
Do test
getAllFuncs([1,3]);
console output:
["constructor", "toString", "toLocaleString", "join", "pop", "push", "concat", "reverse", "shift", "unshift", "slice", "splice", "sort", "filter", "forEach", "some", "every", "map", "indexOf", "lastIndexOf", "reduce", "reduceRight", "entries", "keys", "constructor", "toString", "toLocaleString", "valueOf", "hasOwnProperty", "isPrototypeOf", "propertyIsEnumerable", "__defineGetter__", "__lookupGetter__", "__defineSetter__", "__lookupSetter__"]
Note
It doesn't return functions defined via symbols;
ES6 adds Reflection which makes the code to do this a bit cleaner.
function getAllMethodNames(obj) {
let methods = new Set();
while (obj = Reflect.getPrototypeOf(obj)) {
let keys = Reflect.ownKeys(obj)
keys.forEach((k) => methods.add(k));
}
return methods;
}
/// a simple class hierarchy to test getAllMethodNames
// kind of like an abstract base class
class Shape {
constructor() {}
area() {
throw new Error("can't define area for generic shape, use a subclass")
}
}
// Square: a shape with a sideLength property, an area function and getSideLength function
class Square extends Shape {
constructor(sideLength) {
super();
this.sideLength = sideLength;
}
area() {
return this.sideLength * this.sideLength
};
getSideLength() {
return this.sideLength
};
}
// ColoredSquare: a square with a color
class ColoredSquare extends Square {
constructor(sideLength, color) {
super(sideLength);
this.color = color;
}
getColor() {
return this.color
}
}
let temp = new ColoredSquare(2, "red");
let methods = getAllMethodNames(temp);
console.log([...methods]);