Reconstruct a method from an array of strings and execute it

Question

i have arrays like this: ['req','changepage'] or like this: ['dashboard','draw','ovreview']

the result i need is:

mainObject.req.changepage()

and

mainObject.dashboard.draw.overview()

I know that i can do:

mainObject.[array[0]].[array[1]]()

but the length of the array may vary... how to do that programatically?

• Bergi: Just use a loop?
• user5734311: Here's a solution that uses recursion: jsfiddle.net/khrismuc/jtk9L0ro

Answer 1

You can trivially access a property using reduce:

array.reduce((o, p) => o[p], mainObject)

but to make a method call on the right context object, you need to spare the last property access:

const methodname = array.pop();
array.reduce((o, p) => o[p], mainObject)[methodname]();

Alternatively, use slice if you don't want to mutate the array.

• Bergi: @MaheerAli Otherwise the this keyword in the method doesn't work
• Nina Scholz: no need to pop in advance, the result is a function and the parentheses is the needed call. savind the last key is necessary for assigning a value to it.
• Bergi: @NinaScholz It's also necessary for calling the method as a method, with the object as the context. Otherwise, reduce returns a plain function that would be called with an undefined thisArg.

Answer 2

Besides, Array.reduce, you could just use a loop.

let path = ['first', 'second', 'method'];
let target = {
 first: {
 second: {
 value: 'success',
 method: function(msg) {
 console.log(msg + this.value);
 }
}}};
let result = target;
for (let key of path.slice(0, -1)) {
 result = result[key];
}
result[path.slice(-1)]('result: ') // prints 'result: success'

As Bergi alludes to in their answer, the Array.slice calls (or a use of Array.pop) are needed if the function being called might ever reference this. In my example above, if you just use let key of path, then call result('result: '), the output will be result: undefined.

Answer 3

.reduce is useful for that:

 array.reduce((acc, key) => acc[key], mainObject)();

Or written using a plain for loop:

 let acc = mainObject;
 for(const key of array)
 acc = acc[key];
 acc();