TypeScript Coach

Mapping an array

The map method produces a new array by applying the given function to each element of an existing array.

Consider the following program which applies the result of a function to each element in an array using a for loop, and a more concise way to apply the function with map.

const values = [1, 2, 3, 4, 5]
function square(value: number): number {
    return value * value
}
// Apply the transformation with a for loop
const squaredValues: number[] = []
for (let i = 0 ; i < values.length ; i++) {
    squaredValues.push(square(values[i]))
}
console.log(squaredValues)
// Notice that TypeScript automatically infers the result type
const mappedValues = values.map(square)
console.log(mappedValues)

You can use an inline arrow function with map to quickly transform an array of values.

const values = [ 10, 22, 42, 85, 102 ]
console.log(values.map((value) => Math.sqrt(value)))
console.log(values.map((value) => Math.sqrt(value)))