I want to write a function called printNums() that allows for both:
printNums(1, 2, 3)
printNums([1, 2, 3])
In plain JS, the function would look something like:
function printNums(nums) {
if (!Array.isArray(nums)) {
nums = [...arguments]
}
nums.forEach(num => {
console.log(`Num: ${num}`)
})
}
In TypeScript, how would I write/annotate the nums param?
Easiest way is an overload:
function printNums(...nums: number[]): void;
function printNums(nums: number[]): void;
function printNums(num1: number | number[], ...nums: number[]) {
// safer than using [...arguments].
const normalizedNums = Array.isArray(num1) ? num1 : [num1, ...nums];
normalizedNums.forEach(num => {
console.log(`Num: ${num}`)
})
}
...nums do in the method parameter?
You can use overloads:
function printNums(...nums: number[]): void
function printNums(nums: number[]): void
function printNums(nums: number[] | number) {
if (!Array.isArray(nums)) {
nums = [...arguments] // not type safe but it will work
}
nums.forEach(num => {
console.log(`Num: ${num}`)
})
}
... will cause the data to first be copied to the extra param and then you copy it again to the final array (at least when targeting es5).. not ideal for a large abount of data but depends what you favor, type safety or perf