My cheatsheet of JavaScript functions

Below, you’ll find a few code samples of JavaScript that I often use and would like to save a quick reference.

Does an array contains a value

Use includes if the value to find matches the type of each value in the array.

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const arrayContains = (anArray, myValue) =>
  anArray.includes((item) => item === myValue);

Does an array contains only truthy values

Use reduce with the initial value to true and if all value are true then the result is true too.

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const allButtonsDisabled = (anArrayOfHtmlButton) =>
  anArrayOfHtmlButton.reduce(
    (accumulator, next) => accumulator && next.disabled,
    true
  );

Sum up values

Again, use reduce for this scenario:

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const sum = (anArrayOfNumbers) =>
  anArrayOfNumbers.reduce((total, next) => total + next, 0);

Of course, make sure all values are numbers or floats to avoid issues. For that:

• use the hard way by checking the next variable type and exclude it if not a number (NaN is a number…).
• use the future-proof way with TypeScript to make sure nothing else than a number to be pushed into the array.

Remove an item from an array

Use splice: it is quick and simple to understand.

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const removeItem = (anArray, target) => {
  const targetIndex = anArray.findIndex((itemF) => itemF === target);
  anArray.splice(targetIndex, 1);
};

Extract one property from a list of objects

Use flatMap:

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const extractValuesOfProp = (objectArray, prop) =>
  objectArray.flatMap((object) => object[prop]);

If prop, the value is undefined.

Shuffle values of an array

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const shuffle = (source) => {
  for (let i = source.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [source[i], source[j]] = [source[j], source[i]]; // Swap elements
  }
  return source;
};

More to come…

Save this page as I’ll add more as I practice and work on projects.

Thanks for reading.

Credit: Photo by Sudharshan TK on Unsplash.