freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/drop-it/index.md

title
Drop it

Remember to use Read-Search-Ask if you get stuck. Try to pair program and write your own code

Problem Explanation:

Basically while the second argument is not true, you will have to remove the first element from the left of the array that was passed as the first argument.

Relevant Links

• Arguments object
• Array.shift()
• Array.slice()

Hint: 1

You can use Array.prototype.shift() or filter that you should be more familiar with to solve this problem in a few lines of code.

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Hint: 2

Shift returns the element that was removed which we don't really need, all we need is the modified array that is left.

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Hint: 3

If you still can't figure out how to solve it with shift, then try solving it with filter, and check how filter works, if you become familiar with it, then you can make the code with shift.

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Spoiler Alert!

Solution ahead!

Basic Code Solution:

function dropElements(arr, func) {
  // drop them elements.
  var times = arr.length;
  for (var i = 0; i < times; i++) {
    if (func(arr[0])) {
      break;
    } else {
      arr.shift();
    }
  }
  return arr;
}

// test here
dropElements([1, 2, 3, 4], function(n) {return n >= 3;})

Run Code

Code Explanation:

• Create a for loop to check each element.
• Then check for the function given if true then stop, otherwise remove that element.
• return the array.

Relevant Links

• For Loops
• More about for loops

Intermediate Code Solution:

function dropElements(arr, func) {
  return arr.slice(arr.findIndex(func) >= 0 ? arr.findIndex(func): arr.length, arr.length);
}

// test here
dropElements([1, 2, 3, 4], function(n) {return n >= 3;});

Run Code

Code Explanation:

• Use ES6 findIndex() function to find the index of the element that passes the condition
• Slice the array from the found index until the end
• There is one edge case! if the condition is not met against any of the elements 'findIndex' will return -1 which messes up the input to slice(). In this case use a simple conditional operator to return false instead of -1. And the ternary operator (? returns the found index of required elements when the condition is true, and the length of the array otherwise so that the return value is an empty array as is instructed.

Relevant Links

• findIndex()
• Conditional Operator

Advanced Code Solution:

function dropElements(arr, func) {
  while(arr.length > 0 && !func(arr[0])) {
    arr.shift();
  }
  return arr;
}

// test here
dropElements([1, 2, 3, 4], function(n) {return n >= 3;});

Run Code

Code Explanation

• Use a while loop with Array.prototype.shift() to continue checking and dropping the first element of the array until the function returns true. It also makes sure the array is not empty first to avoid infinite loops.
• Return the filtered array.

Relevant Links

• While loops

NOTES FOR CONTRIBUTIONS:

• DO NOT add solutions that are similar to any existing solutions. If you think it is similar but better, then try to merge (or replace) the existing similar solution.
• Add an explanation of your solution.
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See Wiki Challenge Solution Template for reference.