按条件传参 typescript function

Question

I have function like following. I want to set some value on p3 when a === "add" if a is not equal to "add" just use the default value from function. how can i do it?

function func(p1: string, p2: string, p3: string = 'value'): void{
  console.log(p1);
  console.log(p2);
  console.log(p3);
};

let a = 'add';
func('a', 'b'); // output: a, b, x
let a = 'mins';
func('a', 'b'); // output: a, b, value
// something like
func('a', 'b', (a === "add")? "x") // output: a, b, value

Answer 1

According to the documentation, you can pass undefined to the function and you will use the default specified value:

In TypeScript, we can also set a value that a parameter will be assigned if the user does not provide one, or if the user passes undefined in its place. These are called default-initialized parameters. Let's take the previous example and default the last name to "Smith".

function buildName(firstName: string, lastName = "Smith") {
    return firstName + " " + lastName;
}

let result1 = buildName("Bob");                  // works correctly now, returns "Bob Smith"
let result2 = buildName("Bob", undefined);       // still works, also returns "Bob Smith"

your example should look like this:

func('a', 'b', (a === "add")? "x": undefined)

More here

Answer 2

You can do it like this.

func('a', 'b', ((a === "add") ? "x" : undefined));

But i would prefer this instead.

if (a === 'add') func('a', 'b', 'x');
else func('a', 'b')

Answer 3

In the last line, do this:

func('a', 'b', (a === "add") ? "x" : undefined) // output: a, b, value

But this is not a design that one likes to see in production code or in a code review. Better wrap it in some if/else like so, so that others understand what's going on:

if (a === 'add'){
  func('a', 'b','x');
} else {
  func('a', 'b');
}

Answer 4

you could rewrite your function a little bit to:

function func(p1: string, p2: string, { p3 = 'value' }): void{
  console.log(p1);
  console.log(p2);
  console.log(p3);
};

then you can call it like this:

let a = 'add1'

func("a", "b", (a === 'add' ? { p3: 'hallo' } : {}));