Javascript: How to use object literals instead of if and switch statements for expression-based conditions?

问题

In javascript, I want to at least consider using a nested object literal tree for my control flow instead of if statements, switch statements, etc.

Below is an example of a function using if statements turned into a function using object literals to accomplish the same functionality.

// if & else if
function getDrink (type) {
  if (type === 'coke') {
    type = 'Coke';
  } else if (type === 'pepsi') {
    type = 'Pepsi';
  } else if (type === 'mountain dew') {
    type = 'Mountain Dew';
  } else {
    // acts as our "default"
    type = 'Unknown drink!';
  }
  return type;
}

// object literal
function getDrink (type) {
  var drinks = {
    'coke': function () {
      return 'Coke';
    },
    'pepsi': function () {
      return 'Pepsi';
    },
    'Mountain Dew': function () {
      return 'Mountain dew';
    },
    'default': function () {
      return 'Unknown drink!';
    }
  };
  return (drinks[type] || drinks['default'])();
}

This works when testing for a simple value, but how could I turn the following switch statement into an object literal control structure?

switch (true) {
  case (amount >= 7500 && amount < 10000):
    //code
    break;
  case (amount >= 10000 && amount < 15000):
    //code
    break;

  //etc...

回答1:

A small helper usong Array.find might be useful:

 const firstCase = (...cases) => value => cases.find(c=> c[0](value))[1];

Which is usable as:

const dayTime = firstCase(
  [t =>  t < 5, "night"],
  [t => t < 12, "morning"],
  [t => t < 18, "evening"],
  [true, "night"]
);

console.log(dayTime(10)); // morning

That also works with functions:

const greetAtTime = firstCase(
  [t => t < 10, name => `Good morning ${name}!`],
  [t => t > 18, name => `Good evening ${name}!`],
  [true, name => `Hello ${name}!`]
);

console.log(greetAtTime(12)("Jack"));

回答2:

This appears to work

const getValue = (value) => ({
  [value == 1]: 'Value is 1',
  [value > 1]: 'Value is greater than 1',
  [value < 1]: 'Value is less than 1',
})[true]

console.log(getValue(2));
console.log(getValue(-1)); 
console.log(getValue(-1+2)); // expect 'Value is 1'

来源：https://stackoverflow.com/questions/50817227/javascript-how-to-use-object-literals-instead-of-if-and-switch-statements-for-e

标签

javascript

object

control-flow