Convert string parameter to an array of one element

Question

I wrote a function which has to support two types of a paramter names for a list of values. Internally it deals with the parameter as an array.

A single name is given as string and multiples names are given as an array of strings.

// simplified example let doSome =  names => names.map(name => name.toUpperCase())  names(['Bart', 'Lisa']) // [ 'BART', 'LISA' ] names('Homer') // TypeError: names.map is not a function 

I found a solution using Array.of() in combination with flatten() which needs some babel configuration.

doSome = names => Array.of(names).flatten().map(name => name.toUpperCase()); 

Is there an idiomatic way in JavaScript to get an array without a type check?

Answer 1

You can use Array.concat(), since concat accepts both arrays and non arrays:

const names = (v) => [].concat(v).map(name => name.toUpperCase())    console.log(names(['Bart', 'Lisa'])) // [ 'BART', 'LISA' ]  console.log(names('Homer')) // ['HOMER']

Answer 2

You might not be able to implement it this way if you already have code depending on this function. Still, it would probably be cleaner to allow your function to accept a variable number of arguments with rest parameters.

It means you can call the function as names('Homer') or names('Bart', 'Lisa'):

function names(...args){    return args.map(name => name.toUpperCase());  }    console.log(names('Bart', 'Lisa')); // [ 'BART', 'LISA' ]  console.log(names('Homer')); // ['HOMER']

If you really want to call the function with an array as argument, you can use the spread syntax :

console.log(names(...['Bart', 'Lisa'])); // [ "BART", "LISA" ] 

If you use it with a string, you'll get back an array of characters, though:

console.log(names(...'Homer')); // [ "H", "O", "M", "E", "R" ]