Category: JavaScript Answers

To multiply each member of an array by a scalar in JavaScript, we use the map method.

For instance, we write

const a = [1, 2, 3].map((x) => {
  return x * 5;
});

to call map with a callback to return x in the [1, 2, 3] array being looped through by 5.

An array with each value in [1, 2, 3] multiplied by 5 is returned.

To convert byte array to Hex string conversion in JavaScript, we use the Array.from method.

For instance, we write

const toHexString = (byteArray) => {
  return Array.from(byteArray, (byte) => {
    return `0${(byte & 0xff).toString(16).slice(-2)}`;
  }).join("");
};

to define the toHexString function.

In it, we call Array.from with byteArray and a callback to convert each byte to a hex string.

The callback does a bitwise and with 0xff and then convert that to a hex string with toString called with 16.

And then we get the substring from the 3rd last index to the end of the string with slice.

Then we join the array of hex strings into a string with join.

To find an object in an array by one of its properties with JavaScript, we call the find method.

For instance, we write

const newData = [
  { investor: "Sue", stocks: 0, options: 0, savings: 0 },
  { investor: "Rob", stocks: 0, options: 0, savings: 0 },
  { investor: "Liz", stocks: 0, options: 0, savings: 0 },
];
const investor = "Rob";
const res = newData.find((x) => x.investor === investor);

to call newData.find with a callback that checks whether the investor property in the object being looped through equals to investor.

The first instance of the object where the condition is returned.

To select all other values in an array except the ith element with JavaScript, we use the filter method.

For instance, we write

const items = [1, 2, 3, 4, 5, 6];
const current = 2;
const itemsWithoutCurrent = items.filter((x) => {
  return x !== current;
});

to call items.filter with a callback that checks if x isn’t equal to current and return all the elements in items where x isn’t equal to current.

To create a dynamic array of strings with JavaScript, we just add or remove items as we want.

For instance, we write

const myArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
myArray.push(11);
const popped = myArray.pop();

to call myArray.push with 11 to push a 11 as the last item in myArray.

And we call myArray.pop to remove the last item in myArray and return the removed item.