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    <title>DEV Community: a2br</title>
    <description>The latest articles on DEV Community by a2br (@a2br).</description>
    <link>https://dev.to/a2br</link>
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    <item>
      <title>Get soft IntelliSense when using env vars</title>
      <dc:creator>a2br</dc:creator>
      <pubDate>Wed, 05 May 2021 16:31:46 +0000</pubDate>
      <link>https://dev.to/a2br/a-cool-function-i-m-proud-of-3ncp</link>
      <guid>https://dev.to/a2br/a-cool-function-i-m-proud-of-3ncp</guid>
      <description>&lt;p&gt;Here's a neat function to have some IntelliSense when getting environment variables: it helps, but doesn't prevent you from doing anything it doesn't expect. Go ahead and play with it in the &lt;a href="https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBAYwDYEMDOa4FEB2A3ASyghwFtgcYA1FKLKYqOUGCgE03sbgG8AoAJAISaGFACuCGNAAUAa2ABPAFxxRUAjgDmASl6CBacWGBQZAAwAqAC2DN8cPLQIoARkjsByACQ8FigF9POH84AkxScLRNLQA6cx0AbkEAvlS+AHoMuAB1AiQkOC0CPDsASUpgAoIAZQo0OwAzaDhLABo4V3F4FAQEYDB4AFU+UEhYOBhFEzgAGQJWKBQkIZwCEgAeS2YQVhwOOCGOobgAXjUxGIA+M9a4AB84GROAMjgAJWBhKDYNnGBSlAOv9AVcknxMtkAJoQcRMCiEYhkCgwTwRFBgPhTGa4PC3fhwQlwACyAHkAHIAcVJAH0AIJDSwACVU6hiySJHywABEyjUaQAFHLc1mXbQcokAKRylhpNSwAGF3lhLKKNOK+JzZqTKdzyXSaQBpLBQtXszVEpmkmqWfXErBmjWc8mk7lYGlYclUVQAIjYAKqEDA5EoPoecB9YGIbEkMHWOB9EsJNSG3NpQpFF3VWmSAWS2Lsn2WuNuJbePDgAG1-I6tABdWtwPMQjIAKlbmtbcAAAv60AgNIN461psAALRoFCNOwAdxQikmECKwHgCMctDQnZ7YFoKFIISUrVscDYKBgKDCmCQEAQZ+AbDgZ7g5ijN+AGFiCOrSjr5i33Z3JZ90aZYkFcXo5BJcRRDgHAIHgVw7HMcR9mARpNHvcw4BnWwcDgaD71iVolxQPAIAIB8YGsYgZxiR88NMRgOjAbpnx9H0-zgVsMlGcBoHgRoUKkYcEQ2Q0dj2A5-AgRpsHwDoADEJPYTB5kWZZVnjDZcUrQ06yuK4ZAtQkazmBZTA0tZNkNK42mMuAQIKcCEDkAB+VQlMeGQZD0U4bgUnQ+B0VQ1IslYrJwDY2W0ZT9k4fBdLrOBXLgJTVCLJAdL08MFJuAkiWEHAYNPc9blffoPy-fwkvQD5gGLBLsseFD-XQ-42CTMJZJkEqUD0fLOUJKAVzhPDes6gJmCQBp9EGokCG6xywIgs5TnOFq0Iwtg9ComjYOAGc5MREgQ2oWguFkfxwTmwkFqeAsZIc0DnMgtbzh9QScGEkgfT0JaXtuf6IJ8zrOWGmBRqepyIImtIW2yAVhowOAFTEJAAGoah3fowjw9iOhQfY1GAOwqLsUgUGKBAAEJRnwGQfRdN0PS9H0Og+56IN+1b3p9IA"&gt;TS playground&lt;/a&gt;!&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight typescript"&gt;&lt;code&gt;&lt;span class="c1"&gt;// Will give IntelliSense for T, but accept U&lt;/span&gt;
&lt;span class="k"&gt;export&lt;/span&gt; &lt;span class="kd"&gt;type&lt;/span&gt; &lt;span class="nx"&gt;LiteralUnion&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="nx"&gt;T&lt;/span&gt; &lt;span class="kd"&gt;extends&lt;/span&gt; &lt;span class="nx"&gt;U&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="nx"&gt;U&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="o"&gt;&amp;gt;&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nx"&gt;T&lt;/span&gt; &lt;span class="o"&gt;|&lt;/span&gt; &lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="nx"&gt;U&lt;/span&gt; &lt;span class="o"&gt;&amp;amp;&lt;/span&gt; &lt;span class="nb"&gt;Record&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="nx"&gt;never&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="nx"&gt;never&lt;/span&gt;&lt;span class="o"&gt;&amp;gt;&lt;/span&gt;&lt;span class="p"&gt;);&lt;/span&gt;

&lt;span class="c1"&gt;// Your environment's map&lt;/span&gt;
&lt;span class="kd"&gt;type&lt;/span&gt; &lt;span class="nx"&gt;Env&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt;
    &lt;span class="na"&gt;MONGO_AUTH&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;REDIS_PWD&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;JWT_SECRET&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;LOGDNA_KEY&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;HOSTNAME&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;NODE_ENV&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="dl"&gt;"&lt;/span&gt;&lt;span class="s2"&gt;development&lt;/span&gt;&lt;span class="dl"&gt;"&lt;/span&gt; &lt;span class="o"&gt;|&lt;/span&gt; &lt;span class="dl"&gt;"&lt;/span&gt;&lt;span class="s2"&gt;production&lt;/span&gt;&lt;span class="dl"&gt;"&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="nl"&gt;SUDO_PWD&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
&lt;span class="p"&gt;};&lt;/span&gt;
&lt;span class="kd"&gt;type&lt;/span&gt; &lt;span class="nx"&gt;RealEnv&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nx"&gt;Env&lt;/span&gt; &lt;span class="o"&gt;&amp;amp;&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt; &lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="na"&gt;key&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt;&lt;span class="p"&gt;]:&lt;/span&gt; &lt;span class="kr"&gt;string&lt;/span&gt; &lt;span class="p"&gt;};&lt;/span&gt;

&lt;span class="cm"&gt;/**
 * @description Type-safe way to get env vars
 * @param key The data is located at `process.env[key]`
 * @param fallback Must not be `undefined` when used. To avoid throwing an error, put `""`
 */&lt;/span&gt;
&lt;span class="k"&gt;export&lt;/span&gt; &lt;span class="kd"&gt;function&lt;/span&gt; &lt;span class="nx"&gt;env&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt; &lt;span class="kd"&gt;extends&lt;/span&gt; &lt;span class="kr"&gt;keyof&lt;/span&gt; &lt;span class="nx"&gt;Env&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="nx"&gt;F&lt;/span&gt; &lt;span class="kd"&gt;extends&lt;/span&gt; &lt;span class="nx"&gt;LiteralUnion&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="nx"&gt;Env&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;&lt;span class="o"&gt;&amp;gt;&amp;gt;&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;
    &lt;span class="nx"&gt;key&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="nx"&gt;LiteralUnion&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt;&lt;span class="o"&gt;&amp;gt;&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;
    &lt;span class="nx"&gt;fallback&lt;/span&gt;&lt;span class="p"&gt;?:&lt;/span&gt; &lt;span class="nx"&gt;F&lt;/span&gt; &lt;span class="o"&gt;|&lt;/span&gt; &lt;span class="p"&gt;(()&lt;/span&gt; &lt;span class="o"&gt;=&amp;gt;&lt;/span&gt; &lt;span class="nx"&gt;F&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
&lt;span class="p"&gt;):&lt;/span&gt; &lt;span class="nx"&gt;LiteralUnion&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;&lt;/span&gt;&lt;span class="kr"&gt;string&lt;/span&gt; &lt;span class="kd"&gt;extends&lt;/span&gt; &lt;span class="nx"&gt;Env&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt; &lt;span class="p"&gt;?&lt;/span&gt; &lt;span class="nx"&gt;F&lt;/span&gt; &lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="nx"&gt;RealEnv&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt; &lt;span class="o"&gt;|&lt;/span&gt; &lt;span class="nx"&gt;F&lt;/span&gt;&lt;span class="o"&gt;&amp;gt;&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt;
    &lt;span class="kd"&gt;const&lt;/span&gt; &lt;span class="nx"&gt;data&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nx"&gt;process&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nx"&gt;env&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="nx"&gt;key&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt; &lt;span class="k"&gt;as&lt;/span&gt; &lt;span class="nx"&gt;RealEnv&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="nx"&gt;K&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt; &lt;span class="o"&gt;|&lt;/span&gt; &lt;span class="kc"&gt;undefined&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="nx"&gt;data&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt;
        &lt;span class="k"&gt;return&lt;/span&gt; &lt;span class="nx"&gt;data&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="p"&gt;}&lt;/span&gt; &lt;span class="k"&gt;else&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt;
        &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="nx"&gt;fallback&lt;/span&gt; &lt;span class="o"&gt;===&lt;/span&gt; &lt;span class="kc"&gt;undefined&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt; &lt;span class="k"&gt;throw&lt;/span&gt; &lt;span class="k"&gt;new&lt;/span&gt; &lt;span class="nx"&gt;EnvironmentVarError&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="nx"&gt;key&lt;/span&gt;&lt;span class="p"&gt;);&lt;/span&gt;
        &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="k"&gt;typeof&lt;/span&gt; &lt;span class="nx"&gt;fallback&lt;/span&gt; &lt;span class="o"&gt;===&lt;/span&gt; &lt;span class="dl"&gt;"&lt;/span&gt;&lt;span class="s2"&gt;function&lt;/span&gt;&lt;span class="dl"&gt;"&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt; &lt;span class="nx"&gt;fallback&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nx"&gt;fallback&lt;/span&gt;&lt;span class="p"&gt;();&lt;/span&gt;
        &lt;span class="k"&gt;return&lt;/span&gt; &lt;span class="nx"&gt;fallback&lt;/span&gt;&lt;span class="p"&gt;;&lt;/span&gt;
    &lt;span class="p"&gt;}&lt;/span&gt;
&lt;span class="p"&gt;}&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



</description>
      <category>typescript</category>
      <category>intellisense</category>
      <category>node</category>
      <category>javascript</category>
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