Flatten array of arrays in TypeScript

You can flatten the array with flat()

let foo: string[][] = [["a", "b", "c"], ["a", "b", "c"], ["a", "b", "c"]];
let bar = foo.flat()

log

console.log(bar)   // a,b,c,a,b,c,a,b,c 

UPDATE

By correcting the type to string[] you can also use concat

let foo: string[][] = [["a", "b", "c"], ["a", "b", "c"], ["a", "b", "c"]];
let bar : string[] = []
bar = bar.concat(foo[0], foo[1], foo[2])

Try this:

const a = [["a", "b", "c"], ["a", "b", "c"], ["a", "b", "c"]]
const result = a.reduce((accumulator, value) => accumulator.concat(value), []);
console.log(result)