interview/javascript-interview-flash.html at main · codewreaker/interview · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>JavaScript Interview Flash Sheet</title>
<style>
  body {
    font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
    margin: 32px;
    line-height: 1.35;
    color: #111;
  }
  h1 {
    font-size: 28px;
    margin-bottom: 8px;
  }
  h2 {
    font-size: 18px;
    margin-top: 22px;
    margin-bottom: 6px;
    border-bottom: 1px solid #ddd;
    padding-bottom: 4px;
  }
  .tagline {
    color: #555;
    margin-bottom: 24px;
    font-size: 14px;
  }
  .desc {
    font-size: 14px;
    margin-bottom: 6px;
  }
  ul {
    margin: 6px 0 8px 18px;
    padding: 0;
    font-size: 13px;
  }
  li {
    margin-bottom: 4px;
  }
  pre {
    background: #f6f8fa;
    padding: 10px 12px;
    border-radius: 6px;
    font-size: 12px;
    overflow-x: auto;
    margin: 8px 0 14px 0;
  }
  .two-col {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
  }
  .note {
    font-size: 12px;
    color: #444;
    margin-top: 4px;
  }
  @media print {
    body {
      margin: 20px;
    }
    h2 {
      break-after: avoid;
    }
  }
</style>
</head>
<body>

<h1>JavaScript Interview Flash Sheet</h1>
<div class="tagline">One‑glance reference • Frontend / Systems interviews</div>

<div class="two-col">

<div>
<h2>Event Loop</h2>
<div class="desc">
Runtime model coordinating sync code, async tasks, and rendering.
</div>
<ul>
  <li><strong>Order:</strong> Call Stack → Microtasks → Macrotask → Render</li>
  <li><strong>Microtasks:</strong> Promise.then, queueMicrotask, MutationObserver</li>
  <li><strong>Macrotasks:</strong> setTimeout, setInterval, MessageChannel</li>
</ul>
<pre>
console.log(1);
Promise.resolve().then(() => console.log(2));
setTimeout(() => console.log(3));
// 1, 2, 3
</pre>

<h2>Promises</h2>
<div class="desc">Object representing eventual async result (microtask-based).</div>
<ul>
  <li>Promise.resolve → fulfilled promise</li>
  <li>Promise.reject → rejected promise</li>
  <li>Promise.all → wait all (fail fast)</li>
  <li>Promise.allSettled → all outcomes</li>
  <li>Promise.race → first settled</li>
  <li>Promise.any → first fulfilled</li>
</ul>
<pre>
Promise.all([p1, p2]).then(values => {});
</pre>

<h2>Closures & Scope</h2>
<div class="desc">Function retains access to lexical scope.</div>
<ul>
  <li>Scopes: global, function, block</li>
</ul>
<pre>
function counter() {
  let n = 0;
  return () => ++n;
}
</pre>

<h2>Currying vs Closure vs Thunk</h2>
<ul>
  <li><strong>Closure:</strong> captures state</li>
  <li><strong>Currying:</strong> multi‑arg → chained unary fns</li>
  <li><strong>Thunk:</strong> defers execution</li>
</ul>
<pre>
// Closure
const addX = x => y => x + y;

// Currying
const add = x => y => z => x + y + z;

// Thunk
const thunk = () => expensive();
</pre>
</div>

<div>
<h2>`this`</h2>
<div class="desc">Determined by invocation, not definition.</div>
<ul>
  <li>Function → dynamic this</li>
  <li>Arrow → lexical this</li>
</ul>
<pre>
function show() { return this.x; }

show.call({ x: 1 });
show.apply({ x: 2 });
show.bind({ x: 3 })();
</pre>

<h2>call / apply / bind</h2>
<ul>
  <li>call(this, a, b)</li>
  <li>apply(this, [a, b])</li>
  <li>bind(this) → new fn</li>
</ul>

<h2>Prototypes / Classes</h2>
<div class="desc">
Prototype delegation model. Classes are syntax sugar over prototypes.
</div>

<h2>Equality</h2>
<div class="desc">
=== compares type + value. == allows coercion (avoid).
</div>

<h2>React Fiber</h2>
<div class="desc">
Incremental reconciliation engine.
</div>
<ul>
  <li>Work split into units (fibers)</li>
  <li>Interruptible & resumable</li>
  <li>Priority‑based updates</li>
  <li>Enables concurrent rendering</li>
</ul>

<div class="note">
Interview trap: Fiber ≠ DOM diffing, it’s the scheduling layer.
</div>
</div>

</div>

</body>
</html>