Question 167671 in Javascript Question posted in
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Javascript – Having a problem with rewriting invoke function inspired by underscore library

I’m a beginner and trying to rewrite an underscore function _.invoke.
I’m trying to make the function so it returns an array with the results of calling the method on each value in the collection.

_.invoke = function(collection, methodName) {
  var result = [];
  if (Array.isArray(collection)) {
    for (let i = 0; i < collection.length; i++) {
      methodName.call(collection[i])
      var value = collection[i][methodName]
      result.push(value)
    }
  }
  return result
}

I think my problem lays in this line:

methodName.call(collection[i]) – would like to invoke method on an object collection[i] but I would like to pass some arguments should they be included in the unit test.

I’ve tried so far utilizing the test : typeof(methodName) === "function" and writing a function that would test whether the method is a function.

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2

Answers


  1. 0

    Here you can invoke with arguments.

    _.invoke = function(collection, methodName, ...args) {
  if (!Array.isArray(collection)) {
     return [];
  }
  const out = []; 
  for(const item of collection){
    if(typeof item[methodName] === 'function')
      out.push(item[methodName].apply(item, args));
    }
  }
  return out;
}

    To test that all items have a method:

    const collection = [...];
const allHaveMethod = _.invoke(collection, 'method', 'arg1', 'arg2').length === collection.length;
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  2. 0

    You mean something like this?

    const myArr = [
  { cons:function(args) { return args } },
  { cons:function(args) { return args["bla"] } },
]

const _ = {};
_.invoke = (collection, methodName, ...args) => !Array.isArray(collection) ? [] : collection
.filter(item => typeof item[methodName] === 'function')
.map(item => item[methodName].apply(item, args));

const res = _.invoke(myArr,"cons",{"bla":"hello"})
console.log(res)
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