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Sometimes, we want to find elements in array that are not in another array with JavaScript.

In this article, we’ll look at how to find elements in array that are not in another array with JavaScript.

How to find elements in array that are not in another array with JavaScript?

To find elements in array that are not in another array with JavaScript, we use the filter and includes method.

For instance, we write

const a1 = ["a", "b", "c", "t"];
const a2 = ["d", "a", "t", "e", "g"];

console.log(a2.filter((x) => !a1.includes(x)));

to call filter with a callback that checks if item x in a2 isn’t a1 with includes and negation.

An array with the items in a2 not in a1 is returned.

Conclusion

To find elements in array that are not in another array with JavaScript, we use the filter and includes method.

Sometimes, we want to extract the property values of a JavaScript object into an array.

In this article, we’ll look at how to extract the property values of a JavaScript object into an array.

How to extract the property values of a JavaScript object into an array?

To extract the property values of a JavaScript object into an array, we use the Object.values method.

For instance, we write

const dataObject = {
  object1: {
    id: 1,
    name: "Fred",
  },
  object2: {
    id: 2,
    name: "Wilma",
  },
  object3: {
    id: 3,
    name: "Pebbles",
  },
};

const valuesOnly = Object.values(dataObject);

to call Object.values with dataObject to return the property values of dataObject in an array.

Conclusion

To extract the property values of a JavaScript object into an array, we use the Object.values method.

Sometimes, we want to sort an associative array by its values in JavaScript.

In this article, we’ll look at how to sort an associative array by its values in JavaScript.

How to sort an associative array by its values in JavaScript?

To sort an associative array by its values in JavaScript, we use some object methods.

For instance, we write

const sortedObj = Object.fromEntries(
  Object.entries(data).sort(([, val1], [, val2]) => val1 - val2)
);

to call Object.entries with data to return an array with the key-value pairs in their own arrays.

Then we call sort with a callback that gets the property values from each array and compare them to do the sorting and return the sorted array.

Then we call Object.fromEntries to convert the array of key-value pair arrays back into an object.

Conclusion

To sort an associative array by its values in JavaScript, we use some object methods.

Sometimes, we want to populate drop down list with array with JavaScript.

In this article, we’ll look at how to populate drop down list with array with JavaScript.

How to populate drop down list with array with JavaScript?

To populate drop down list with array with JavaScript, we call the createElement method.

For instance, we write

const arr = ["1", "2", "3", "4"];
arr.forEach((item) => {
  const optionObj = document.createElement("option");
  optionObj.textContent = item;
  document.getElementById("myselect").appendChild(optionObj);
});

to call arr.forEach with a callback that calls createElement to create an option element.

Then we set the text of the option by setting the textContent property.

Then we select the select element and append the option element to it with appendChild.

Conclusion

To populate drop down list with array with JavaScript, we call the createElement method.

Sometimes, we want to detect if argument is array instead of object with Node.js.

In this article, we’ll look at how to detect if argument is array instead of object with Node.js.

How to detect if argument is array instead of object with Node.js?

To detect if argument is array instead of object with Node.js, we use the util.isArray method.

For instance, we write

const util = require("util");

const isArray = util.isArray([]);

to call util.isArray with an empty array to check if the argument is an array.

true is returned if it is.

Conclusion

To detect if argument is array instead of object with Node.js, we use the util.isArray method.