I have a variable foo to be initialized. My attempt below does not compile.

let foo: (x: number)=>{y:number,z: number}= (x)=>{x 1,x 2};

with the following error:

Left side of comma operator is unused and has no side effects.ts(2695) (parameter) x: number

Question

What is the correct way to initialize the variable foo?

CodePudding user response：

Because of how arrow function notation works, the curly braces around the output are interpreted as containing the function body instead of a value being returned.

It also looks like you've forgot to add the y and z labels in your output.

Try this:

let foo: (x: number) => {y: number, z: number} = (x) => {
    return {y: x 1, z: x 2};
};

It's also worth noting that when initialising a variable in this way, TypeScript is able to infer its type. So you can actually shorten your code to just this:

let foo = (x: number) => {
    return {y: x 1, z: x 2};
};