Merge pull request #250 from asemarian/master

book6, ch4: 5 new questions

src/data/ES6Beyond/ch4.js

@@ -20,6 +20,21 @@ const Ch4Questions = [
     explanation:
       'If there are no errors, then the Promise will get resolved, but if an error occurs typically the Promise will get rejected.',
   },
+  {
+    question: 'A promise can only be resolved (fulfilled or rejected) once',
+    questionId: 'Llq2fzjMh81c6BpCh5Dq',
+    shouldBeRandomized: false,
+    answers: [
+      {
+        text: 'True',
+        id: 0,
+      },
+      { text: 'False', id: 1 },
+    ],
+    correctAnswerId: 0,
+    moreInfoUrl: 'https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch4.md#promises',
+    explanation: "Promises can only be resolved (fulfillment or rejection) once. Any further attempts to fulfill or reject are simply ignored. Thus, once a Promise is resolved, it's an immutable value that cannot be changed."
+  },
   {
     question: `This is a valid way to construct a promise:
 ${'```js'}
@@ -70,6 +85,32 @@ ${'```'}
     explanation:
       '`done` is not a valid method for a Promise. The code above would be valid if it were replaced with `.then()`',
   },
+  {
+    question: 'What do `.then(..)` and `.catch(..)` methods return when invoked on a promise?',
+    questionId: 'dyrVkcETZ8s7ipq1ieZ3',
+    shouldBeRandomized: true,
+    answers: [
+      {
+        text: 'another promise',
+        id: 0
+      },
+      {
+        text: 'an object',
+        id: 1
+      },
+      {
+        text: '`undefined`',
+        id: 2
+      },
+      {
+        text: 'a function',
+        id: 3
+      }
+    ],
+    correctAnswerId: 0,
+    moreInfoUrl: 'https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch4.md#making-and-using-promises',
+    explanation: "Both `then(..)` and `catch(..)` automatically construct and return another promise instance, which is wired to receive the resolution from whatever the return value is from the original promise's fulfillment or rejection handler (whichever is actually called)"
+  },
   {
     question: `What are thenables?`,
     questionId: 'fw3mKgWDPvDorEt1J7gi',
@@ -121,6 +162,89 @@ ${'```'}
     explanation:
       '`Promise.resolve` creates a resolved promise. To access the value `42`, you need to call `.then()`',
   },
+  {
+    question: `What will be logged to the console when the following is executed?
+  ${'```js'}
+  const a = 42, b = Promise.resolve(43), c = 44;
+  Promise.all([a, b, c]).then(val => console.log(val));
+  ${'```'}  
+    `,
+    questionId: '2eNwGVoqyK8G9fTf8aBX',
+    shouldBeRandomized: true,
+    answers: [
+      {
+        text: '`42`',
+        id: 0
+      },
+      {
+        text: '`43`',
+        id: 1
+      },
+      {
+        text: '`[42, 43, 44]`',
+        id: 2
+      }
+    ],
+    correctAnswerId: 2,
+    moreInfoUrl: 'https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch4.md#promise-api',
+    explanation: "`Promise.all([ .. ])` accepts an array of one or more values (e.g., immediate values, promises, thenables). It returns a promise back that will be fulfilled if all the values fulfill, or reject immediately once the first of any of them rejects"
+  },
+  {
+    question: `What will be logged to the console when the following is executed?
+  ${'```js'}
+  const a = 42, b = Promise.resolve(43), c = 44;
+  Promise.race([a, b, c]).then(val => console.log(val));
+  ${'```'}  
+    `,
+    questionId: 'CjctOIwGZTztV155yKQC',
+    shouldBeRandomized: true,
+    answers: [
+      {
+        text: '`42`',
+        id: 0
+      },
+      {
+        text: '`43`',
+        id: 1
+      },
+      {
+        text: '`[42, 43, 44]`',
+        id: 2
+      }
+    ],
+    correctAnswerId: 0,
+    moreInfoUrl: 'https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch4.md#promise-api',
+    explanation: "While `Promise.all([ .. ])` waits for all fulfillments (or the first rejection), `Promise.race([ .. ])` waits only for either the first fulfillment or rejection."
+  },
+  {
+    question: `What will be logged to the console when the following is executed?
+  ${'```js'}
+  const a = Promise.resolve(43), b = 42, c = Promise.reject("Oops");
+  Promise.race([a, b, c])
+  .then(val => console.log(val))
+  .catch(e => console.log(e));
+  ${'```'}  
+    `,
+    questionId: 'H9b44hy04P9rCW5TGewO',
+    shouldBeRandomized: true,
+    answers: [
+      {
+        text: '`42`',
+        id: 0
+      },
+      {
+        text: '`43`',
+        id: 1
+      },
+      {
+        text: '`"Oops"`',
+        id: 2
+      }
+    ],
+    correctAnswerId: 1,
+    moreInfoUrl: 'https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch4.md#promise-api',
+    explanation: "While `Promise.all([ .. ])` waits for all fulfillments (or the first rejection), `Promise.race([ .. ])` waits only for either the first fulfillment or rejection (whichever happens first). In the code snippet above, if we changed the order of the array to `Promise.race([c, b, a])` then we'd get `'Oops'` printed instead."
+  }
 ];
 
 export default Ch4Questions;