manual-javascript
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JavaScript 是一种具有函数优先的轻量级、解释型、即时编译型的编程语言。
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<h1 id="基本数据类型">基本数据类型</h1>
<p>JavaScript 中的基本数据类型主要包括数值类型、字符串类型、布尔类型、未定义类型、空类型。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> num <span class="token operator">=</span> <span class="token number">233</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num<span class="token punctuation">,</span> <span class="token keyword">typeof</span> num<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> bin <span class="token operator">=</span> <span class="token number">0b10101</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>bin<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> oct <span class="token operator">=</span> <span class="token number">0o777</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>oct<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> hex <span class="token operator">=</span> <span class="token number">0xff</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>hex<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> str <span class="token operator">=</span> <span class="token string">'Hello World!'</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>str<span class="token punctuation">,</span> <span class="token keyword">typeof</span> str<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> bool <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>bool<span class="token punctuation">,</span> <span class="token keyword">typeof</span> bool<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> undef<span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>undef<span class="token punctuation">,</span> <span class="token keyword">typeof</span> undef<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> <span class="token constant">NULL</span> <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token constant">NULL</span><span class="token punctuation">,</span> <span class="token keyword">typeof</span> <span class="token constant">NULL</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>BigInt 数据类型是比数值类型支持范围更大的整数值。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> num1 <span class="token operator">=</span> <span class="token number">233n</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num1<span class="token punctuation">,</span> <span class="token keyword">typeof</span> num1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> num2 <span class="token operator">=</span> <span class="token function">BigInt</span><span class="token punctuation">(</span><span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>num2<span class="token punctuation">,</span> <span class="token keyword">typeof</span> num2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> max <span class="token operator">=</span> Number<span class="token punctuation">.</span><span class="token constant">MAX_SAFE_INTEGER</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token function">BigInt</span><span class="token punctuation">(</span>max<span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token function">BigInt</span><span class="token punctuation">(</span>max<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>ES6 中新增了用于存储唯一值的集合数据类型。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> <span class="token keyword">set</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Set</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">,</span> <span class="token number">1.23</span><span class="token punctuation">,</span> <span class="token number">233</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">.</span>size<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> v <span class="token keyword">of</span> <span class="token keyword">set</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">set</span><span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">'Hello World!'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">set</span><span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token number">666</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span><span class="token number">233</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">set</span><span class="token punctuation">.</span><span class="token function">clear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">set</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>ES6 中还新增了用于存储键值对的映射数据类型。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token string">'name'</span><span class="token punctuation">,</span> <span class="token string">'Tom'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token string">'func'</span><span class="token punctuation">,</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token string">'Hello World!'</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
foo<span class="token operator">:</span> <span class="token string">'bar'</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">233</span><span class="token punctuation">,</span> <span class="token number">666</span><span class="token punctuation">,</span> <span class="token number">1.23</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span>size<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> v <span class="token keyword">of</span> map<span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">'name'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">'func'</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token string">'name'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">)</span><span class="token punctuation">;</span>
map<span class="token punctuation">.</span><span class="token function">clear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>map<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>Symbol 是 JavaScript 中一种不可变且唯一的数据类型，通常用来创建独一无二的键。</p>
<pre class="language-"><code class="lang-javascript"><span class="token keyword">let</span> symbol1 <span class="token operator">=</span> <span class="token function">Symbol</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>symbol1<span class="token punctuation">,</span> <span class="token keyword">typeof</span> symbol1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> symbol2 <span class="token operator">=</span> <span class="token function">Symbol</span><span class="token punctuation">(</span><span class="token string">'Hello'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>symbol2<span class="token punctuation">,</span> <span class="token keyword">typeof</span> symbol2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> symbol3 <span class="token operator">=</span> <span class="token function">Symbol</span><span class="token punctuation">(</span><span class="token string">'JavaScript'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>symbol3<span class="token punctuation">,</span> <span class="token keyword">typeof</span> symbol3<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
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