Javascript:如何为基于表达式的条件使用对象文字而不是 if 和 switch 语句? [英] Javascript: How to use object literals instead of if and switch statements for expression-based conditions?

问题描述

在 javascript 中，我至少要考虑使用嵌套对象字面量树作为我的控制流，而不是 if 语句、switch 语句等.

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.

下面是一个使用 if 语句的函数转换为使用对象字面量完成相同功能的函数的示例.

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'])();
}

这在测试简单值时有效，但如何将以下 switch 语句转换为对象字面量控制结构?

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...

推荐答案

一个使用 Array.find 的小帮手可能会有用:

A small helper usong Array.find might be useful:

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

可用作:

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

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

这也适用于函数:

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"));

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