Imports and webpack contexts

index.md

Imports and webpack contexts

This is an example to my article “How webpack’s ContextReplacementPlugin works”

Each time webpack encounters a dynamic import like this:

require('./locale/' + name + '.js')

it extracts from it three pieces of information:

• directory in which to search for the files (./locale)
• regular expression to test the files against (/^.*\.js)
• and if webpack should look for the files in the subdirectories (always true by default).

Here’re some examples of dynamic imports and corresponding contexts.

---

require(path);

When you specify only a single variable, there isn’t enough information for webpack to create a context. You’ll see the following warning when doing a build:

WARNING in ./index.js
Critical dependency: the request of a dependency is an expression

---

require(path + '.js');

regular expression: ^.*\.js$, recursive: true

---

require(path + '/index.js');

regular expression: ^.*\/index\.js$, recursive: true

---

require('./existing-directory/' + path + '/index.js');

regular expression: ^.*\/index\.js$, directory: absolute path of ./existing-directory, recursive: true

---

require('./non-existing-directory/' + path + '/index.js');

You’ll see the following error when doing a build:

Module not found: Error: Can't resolve './non-existing-directory' in '<absolute-path>/index.js'

---

require(part1 + 'staticPart2' + part3 + '.js');

regular expression: ^.*\.js$, recursive: true (All the expressions in the middle of concatenation are not evaluated.)

---

require('./existing-directory/' + part1 + 'staticPart2' + part3 + '.js');

regular expression: ^.*\.js$, directory: absolute path of ./existing-directory, recursive: true (All the expressions in the middle of concatenation are not evaluated.)

---

require(flag ? 'staticPathA' : 'staticPathB');
require('staticPathA' + 'staticPathB');
require('staticPathA'.substr(0, 5));

These are simpler expressions that don’t require creating a context. See parser evaluation

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