Category: JavaScript Answers

To check if the JavaScript array of objects have duplicate property values, we can compare its size to its set equivalent.

For instance, we write

const values = [
  { name: "name1" },
  { name: "name2" },
  { name: "name3" },
  { name: "name1" },
];

const uniqueValues = new Set(values.map((v) => v.name));

if (uniqueValues.size < values.length) {
  console.log("duplicates found");
}

to create a set with the Set constructor with an array of name property values from each object.

Then we compare the size of the set to the length of the array to check if there’re any duplicates.

If the size of the set is smaller than the array’s length, then there are duplicates.

To sort JavaScript array by two numeric fields, we call the sort method.

For instance, we write

const sorted = grouperArray.sort((a, b) => {
  return a.size - b.size || a.glow - b.glow;
});

to call sort with a callback that compares the items by their size property values and glow property values.

To upload multiple files using JavaScript formData, we call append with an array key.

For instance, we write

fd.append("fileToUpload[]", document.getElementById("fileToUpload").files[0]);

to call fd.append with the "fileToUpload[]" array key and a file we get from a file input.

We get the file input with getElementById.

And we get the selected files from the files property.

To sort a JavaScript array based on the length of each element, we call the sort method.

For instance, we write

const sorted = arr.sort((a, b) => {
  return b.length - a.length;
});

to call arr.sort with a callback that subtracts the length property values of b and a to return an array with the strings in arr sorted by length in descending order.

To remove first and last element in a JavaScript array, we use shift to remove the first item and pop to remove the last item.

For instance, we write

const fruits = ["Banana", "Orange", "Apple", "Mango"];

fruits.shift();
fruits.pop();

to call fruits.shift to remove the first item from fruits.

And we call fruits.pop to remove the last item from fruits.