I want to set a variable based on the result of a function call.. I don't want to call the function two times, or add an unncessary "temporary" variable to the function scope. I know it's probably premature optimization but I like doing that.
I can use the temporary variable obj inside a block scope like this:
function foo(){
let output;
calculate_output: {
const obj = get_object();
if(obj.x > obj.y){
output = "x is greater than y";
}else if(obj.x < obj.y){
output = "x is less than y";
}else{
output = "x is equal to y";
}
}
console.log(output);
// more code that uses [output] below, so I don't want an unnecessary [obj] cluttering the function scope here..
}
But in order to do that, I have to make output a let which is.. wrong. It won't change value, so I want it to be a const.
The only way I know how to achieve this involves calling the function multiple times, like this:
const output = get_object().x > get_object().y ? "x is greater than y" : get_object().x < get_object().y ? "etc";
So is there another way I can calculate the value of output with temporary variables? Something like this:
const output = (const obj = get_object(); obj.x > obj.y ? "x is greater than y" : obj.x < obj.y ? "etc");
Your use of let is the clearest way to do it, IMHO. There's no way to declare a variable that can be assigned only once and must remain read-only after that.
If you really want to use const, you could do it with ternaries in the initialization expression.
function foo() {
const obj = get_object();
const output = obj.x > obj.y ?
"x is greater than y" : (
obj.x < obj.y ?
"x is less than y" : "x is equal to y"
);
console.log(output);
}If the initialization requires even more complex logic, you could use an IIFE.