Flatten arbitrary array of numbers in Typescript / Angular

flattenArray.ts

testArray:Array<any> = [10, [9,8,7],6, [5, [4,3,2], 1], 10,9,8];

flatten(list:Array<any>) {
		let flattened:Array<number> = [];

		// For each item in the provided list, check to see if it's a number.
		// if it's not, recurse with the sub-array and add those items.
		for (let item of list) {
			if (typeof item === "number") {
				flattened.push(item);
			} else {
				flattened = [...flattened, ...this.flatten(item)];
			}
		}
		return flattened;
	}
  
let flattenedArray = this.flatten(this.testArray);
console.log(flattenedArray);