freeCodeCamp/using-objects-for-lookups.md at 41b7a331008a97d20155c3752b3beb530375ab99

Oliver Eyton-Williams 41b7a33100

fix: replace .chinese.md extension with .md

2020-09-29 22:09:05 +02:00

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Raw Blame History

id, title, challengeType, videoUrl, forumTopicId, localeTitle

id	title	challengeType	videoUrl	forumTopicId	localeTitle
56533eb9ac21ba0edf2244ca	Using Objects for Lookups	1	https://scrimba.com/c/cdBk8sM	18373	使用对象进行查找

Description

对象和字典一样，可以用来存储键/值对。如果你的数据跟对象一样，你可以用对象来查找你想要的值，而不是使用switch或if/else语句。当你知道你的输入数据在某个范围时，这种查找方式极为有效。这是简单的反向字母表：

var alpha = {
  1:"Z",
  2:"Y",
  3:"X",
  4:"W",
  ...
  24:"C",
  25:"B",
  26:"A"
};
alpha[2]; // "Y"
alpha[24]; // "C"

var value = 2;
alpha[value]; // "Y"

Instructions

把 switch 语句转化为lookup对象。使用它来查找val属性的值，并赋值给result变量。

Tests

tests:
  - text: <code>phoneticLookup("alpha")</code>应该等于<code>"Adams"</code>。
    testString: assert(phoneticLookup("alpha") === 'Adams');
  - text: <code>phoneticLookup("bravo")</code>应该等于<code>"Boston"</code>。
    testString: assert(phoneticLookup("bravo") === 'Boston');
  - text: <code>phoneticLookup("charlie")</code>应该等于<code>"Chicago"</code>。
    testString: assert(phoneticLookup("charlie") === 'Chicago');
  - text: <code>phoneticLookup("delta")</code>应该等于<code>"Denver"</code>。
    testString: assert(phoneticLookup("delta") === 'Denver');
  - text: <code>phoneticLookup("echo")</code>应该等于<code>"Easy"</code>。
    testString: assert(phoneticLookup("echo") === 'Easy');
  - text: <code>phoneticLookup("foxtrot")</code>应该等于<code>"Frank"</code>。
    testString: assert(phoneticLookup("foxtrot") === 'Frank');
  - text: <code>phoneticLookup("")</code>应该等于<code>undefined</code>。
    testString: assert(typeof phoneticLookup("") === 'undefined');
  - text: 请不要修改<code>return</code>语句。
    testString: assert(code.match(/return\sresult;/));
  - text: 请不要使用<code>case</code>，<code>switch</code>，或<code>if</code>语句。
    testString: assert(!/case|switch|if/g.test(code.replace(/([/]{2}.*)|([/][*][^/*]*[*][/])/g,'')));

Challenge Seed

// Setup
function phoneticLookup(val) {
  var result = "";

  // Only change code below this line
  switch(val) {
    case "alpha":
      result = "Adams";
      break;
    case "bravo":
      result = "Boston";
      break;
    case "charlie":
      result = "Chicago";
      break;
    case "delta":
      result = "Denver";
      break;
    case "echo":
      result = "Easy";
      break;
    case "foxtrot":
      result = "Frank";
  }

  // Only change code above this line
  return result;
}

// Change this value to test
phoneticLookup("charlie");

Solution

function phoneticLookup(val) {
  var result = "";

  var lookup = {
    alpha: "Adams",
    bravo: "Boston",
    charlie: "Chicago",
    delta: "Denver",
    echo: "Easy",
    foxtrot: "Frank"
  };

  result = lookup[val];

  return result;
}

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