node.js process.env：将 process.env 属性分配给未定义的字符串类型结果？

Question

The node.js process.env object seems to process property assignment differently than regular JavaScript objects. How can I get the process.env object to act like a regular object in this case?

Below is sample code illustrating the different assignment behavior. For some reason assigning undefined to a property results in a string type (only for process.env ):

function demo(description, dict) {
    console.log(description);
    dict.A = undefined;
    console.log('typeof dict.A: ' + typeof dict.A + '\n');
}
demo('Passing empty object:', {});
demo('Passing process.env:',  process.env);

The resulting output is different depending on if an empty object {} or the process.env object was passed:

$ node test.js
Passing empty object:
typeof dict.A: undefined

Passing process.env:
typeof dict.A: string

Answer 1

The process.env object forces all of its properties to be of type string, since environment variables must always be strings. I'm not entirely sure on your purpose, but maybe you could try one of these as a workaround:

• Copy the process.env object into a new object, which will then behave normally:

   envCopy = {}; for (e in process.env) envCopy[e] = process.env[e]; 

• Assign '' to a property instead if you wish it to be 'blank'

   process.env.A = ''; 

  Which will then return false when you treat it as a boolean

   if (process.env.A) { ... } 

• Or as Jonathan Lonowski points out, you can also delete the key from process.env

   delete process.env.A; 

Hope this helps

Answer 2

This is occurring because process.env forces all of its values to String :

process.env.A = undefined;
console.log(process.env.A);        // 'undefined' (note the quotes)

process.env.A = true;
console.log(process.env.A);        // 'true'
console.log(typeof process.env.A); // 'string'

If you need to remove an environment variable, you'll have to delete it:

function demo(description, dict) {
    console.log(description);
    delete dict.A;
    console.log('typeof dict.A: ' + typeof dict.A + '\n');
}
demo('Passing process.env:', process.env);

// Passing process.env:
// typeof dict.A: undefined

Answer 3

You can bypass process.env 's string coercion by using Object.defineProperty instead:

Object.defineProperty(process.env, 'ENV_VAR_NAME', {
  configurable: true,
  value: nonStringValue
});

configurable: true is required if you want to do delete process.env.ENV_VAR_NAME later on.