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JavaScript: Mutate the original array to filter out the values specified, based on a given iterator function

JavaScript fundamental (ES6 Syntax): Exercise-160 with Solution

Write a JavaScript program to mutate the original array to filter out the values specified, based on a given iterator function.

  • Check if the last argument provided is a function.
  • Use Array.prototype.map() to apply the iterator function fn to all array elements.
  • Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed.
  • Set Array.prototype.length to mutate the passed in an array by resetting its length to 0.
  • Use Array.prototype.push() to re-populate it with only the pulled values.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const pullBy = (arr, ...args) => {
  const length = args.length;
  let fn = length > 1 ? args[length - 1] : undefined;
  fn = typeof fn == 'function' ? (args.pop(), fn) : undefined;
  let argState = (Array.isArray(args[0]) ? args[0] : args).map(val => fn(val));
  let pulled = arr.filter((v, i) => !argState.includes(fn(v)));
  arr.length = 0;
  pulled.forEach(v => arr.push(v));
};

var myArray = [{ x: 1 }, { x: 2 }, { x: 3 }, { x: 1 }];

pullBy(myArray, [{ x: 1 }, { x: 3 }], o => o.x);

console.log(myArray);

Sample Output:

[{"x":2}]

Pictorial Presentation:

JavaScript Fundamental: Mutate the original array to filter out the values specified, based on a given iterator function.

Flowchart:

flowchart: Mutate the original array to filter out the values specified, based on a given iterator function

Live Demo:

See the Pen javascript-basic-exercise-160-1 by w3resource (@w3resource) on CodePen.


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JavaScript: Tips of the Day

Checking if a key exists in a JavaScript object?

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?

var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!

You should instead use the in operator:

"key" in obj // true, regardless of the actual value

If you want to check if a key doesn't exist, remember to use parenthesis:

!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:

obj.hasOwnProperty("key") // true

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists! You should instead use the in operator: "key" in obj // true, regardless of the actual value If you want to check if a key doesn't exist, remember to use parenthesis: !("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj" Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty: obj.hasOwnProperty("key") // true For performance comparison between the methods that are in, hasOwnProperty and key is undefined.

Ref: https://bit.ly/2CFNp1X