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JavaScript: Remove elements from the end of an array until the passed function returns true

JavaScript fundamental (ES6 Syntax): Exercise-242 with Solution

Write a JavaScript program to remove elements from the end of an array until the passed function returns true. Returns the remaining elements in the array.

  • Loop through the array, using Array.prototype.slice() to drop the last element of the array until the value returned from func is true.
  • Return the remaining elements.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const dropRightWhile = (arr, func) => {
  while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
  return arr;
};

console.log(dropRightWhile([1, 2, 3, 4], n => n < 3));

Sample Output:

[1,2]

Flowchart:

flowchart: Remove elements from the end of an array until the passed function returns true.

Live Demo:

See the Pen javascript-basic-exercise-242-1 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