how to pass not mandatory param in function angular code example

Example 1: how to make a parameter optional in typescript

// Optional parameter
function foo(x?: number) {
    console.log("x : "+ x);
}
foo();
foo(6);

Example 2: typescript make function argument optional

function multiply(a: number, b: number, c?: number): number {

    if (typeof c !== 'undefined') {
        return a * b * c;
    }
    return a * b;
}