Get functions (methods) of a class
JavascriptOopEcmascript 6Javascript Problem Overview
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
Javascript Solutions
Solution 1 - Javascript
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.
Solution 2 - Javascript
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;
Solution 3 - Javascript
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]);
Solution 4 - Javascript
There were a few issues in @MuhammadUmer answer for me (symbols, index i+1
, listing of Object
methods, etc...) so taking inspiration from it, I came up with this
(warning Typescript compiled to ES6)
const getAllMethods = (obj) => {
let props = []
do {
const l = Object.getOwnPropertyNames(obj)
.concat(Object.getOwnPropertySymbols(obj).map(s => s.toString()))
.sort()
.filter((p, i, arr) =>
typeof obj[p] === 'function' && //only the methods
p !== 'constructor' && //not the constructor
(i == 0 || p !== arr[i - 1]) && //not overriding in this prototype
props.indexOf(p) === -1 //not overridden in a child
)
props = props.concat(l)
}
while (
(obj = Object.getPrototypeOf(obj)) && //walk-up the prototype chain
Object.getPrototypeOf(obj) //not the the Object prototype methods (hasOwnProperty, etc...)
)
return props
}
This function will list all methods of an instance of the class including those inherited, but not the constructor and those of the Object prototype.
Test
The function returns
[ 'asyncMethod', 'echo', 'generatorMethod', 'ping', 'pong', 'anotherEcho' ]
listing the methods of an instance of TestClass
(typescript)
class Echo {
echo(data: string): string {
return data
}
anotherEcho(data: string): string {
return `Echo ${data}`
}
}
class TestClass extends Echo {
ping(data: string): string {
if (data === 'ping') {
return 'pong'
}
throw new Error('"ping" was expected !')
}
pong(data: string): string {
if (data === 'pong') {
return 'ping'
}
throw new Error('"pong" was expected !')
}
//overridden echo
echo(data: string): string {
return 'blah'
}
async asyncMethod(): Promise<string> {
return new Promise<string>((resolve: (value?: string) => void, reject: (reason?: any) => void) => {
resolve('blah')
})
}
* generatorMethod(): IterableIterator<string> {
yield 'blah'
}
}
Solution 5 - Javascript
To make members of class enumerable you can use Symbol.iterator
I had to get all allowed methods of object (including inherited). So i created class "Enumerable" and all my base classes inherited from him.
class Enumerable {
constructor() {
// Add this for enumerate ES6 class-methods
var obj = this;
var getProps = function* (object) {
if (object !== Object.prototype) {
for (let name of Object.getOwnPropertyNames(object)) {
let method = object[name];
// Supposedly you'd like to skip constructor and private methods (start with _ )
if (method instanceof Function && name !== 'constructor' && name[0] !== '_')
yield name;
}
yield* getProps(Object.getPrototypeOf(object));
}
}
this[Symbol.iterator] = function*() {
yield* getProps(obj);
}
// --------------
}
}