How to use CONST when there are multiple conditions

问题

I'm getting on the const train and want to start avoiding let at all costs.

The problem I'm seeing is the below case - how would I use const in a situation with more than 2 forks in a logic tree?

What's the equivalent pattern with const?

function getResult(input) {
    let result;

    switch (input): {
        case (1): { result=x;}
        case (2): { result=y;}
        case (3): { result=x;}
        ...etc
    }

    /*
    ...additional conditionals and functions depending on the outcomes 
    of switch statement
    */    
}

thanks,

回答1:

 const result = [x,y,x][input - 1];

It's an array that's accessed by index.

回答2:

There is nothing wrong with using let in this case. Const is useful for creating non changing variables throughout the file, function or class. For example, storing a non changing base url for http calls (https://your.domain.here/).

Whereas let and var are more suited to changing variables such as the amount of time a user clicks on a button, or slider to select a minimum and maximum date/age range.

However, you will want to change your switch statement to a valid statement like so:

switch (input) {
    case 1: {
        result=x;
        break;
    }
    case 2: {
        result=y;
        break;
    }
    case 3: {
        result=x;
        break;
    }
    default:
        break;
}

回答3:

While I don't necessarily agree with "avoiding let at all cost", I'd say the best alternative for using a switch statement is to put it in a separate function and use return.

The example below shows a pure inner result function that holds the switch logic. Instead of assigning to a variable, it returns a result as soon as it finds a match.

const getInnerResult = (x, y, input) => {
  switch (input) { 
    case 1: 
    case 3:  return x;
    case 2:  return y;
    default: return null; 
  }
}

const getResult = function(input) {
  const result = getInnerResult("a", "b", input);
  
  // Other logic using the `result` variable
  return result ? result.toUpperCase() : "-";
};


console.log(getResult(2));
console.log(getResult(5));

来源：https://stackoverflow.com/questions/48503199/how-to-use-const-when-there-are-multiple-conditions

标签

javascript

functional-programming

const