We can use the Object.getOwnPropertyNames() function to get all the property names linked to an object.

Then we can filter the resulting array, to only include that property name if it’s a function.

We determine if it’s a function by using typeof on it.

For example here is how we might create a utility function to do what we need:

getMethods = (obj) => Object.getOwnPropertyNames(obj).filter(item => typeof obj[item] === 'function')


This lists only the methods defined on that specific object, not any method defined in its prototype chain.

To do that we must take a slightly different route. We must first iterate the prototype chain and we list all the properties in an array. Then we check if each single property is a function.

An easy way to make sure we don’t duplicate methods as we navigate the prototype chain (like constructor which is always present), we use a Set data structure that makes sure values are unique:

const getMethods = (obj) => {
let properties = new Set()
let currentObj = obj
do {
} while ((currentObj = Object.getPrototypeOf(currentObj)))
return [...properties.keys()].filter(item => typeof obj[item] === 'function')
}


Example usage:

getMethods("")
getMethods(new String('test'))
getMethods({})
getMethods(Date.prototype)