feat: Support string as an argument to the tag function (#132)

Author: fatfisz

readme.md

@@ -48,6 +48,7 @@
       - [`oneLineCommaListsAnd`](#onelinecommalistsand)
 - [:wrench: Advanced Usage](#wrench-advanced-usage)
     - [Tail Processing](#tail-processing)
+    - [Calling with strings](#calling-with-strings)
     - [Make Your Own Template Tag](#make-your-own-template-tag)
       - [Class is in Session: TemplateTag](#class-is-in-session-templatetag)
       - [The Anatomy of a Transformer](#the-anatomy-of-a-transformer)
@@ -482,6 +483,20 @@ oneLine(String.raw)`
 
 
 
+
+### Calling with strings
+
+Sometimes you might want to use a tag on a normal string (e.g. for stripping the indentation). For that purpose just call a tag as a function with the passed string:
+
+```js
+import {stripIndent} from 'common-tags'
+
+stripIndent("  foo\n    bar")
+// "foo\n  bar"
+```
+
+
+
 ### Make Your Own Template Tag
 
 `common-tags` exposes an interface that allows you to painlessly create your own template tags.

src/TemplateTag/TemplateTag.js

@@ -13,7 +13,7 @@ export default class TemplateTag {
    */
   constructor (...transformers) {
     // if first argument is an array, extrude it as a list of transformers
-    if (transformers.length && Array.isArray(transformers[0])) {
+    if (transformers.length > 0 && Array.isArray(transformers[0])) {
       transformers = transformers[0]
     }
 
@@ -32,21 +32,26 @@ export default class TemplateTag {
    * Applies all transformers to a template literal tagged with this method.
    * If a function is passed as the first argument, assumes the function is a template tag
    * and applies it to the template, returning a template tag.
-   * @param  {(Function|Array<String>)} args[0] - Either a template tag or an array containing template strings separated by identifier
-   * @param  {...*} [args[1]]                   - Optional list of substitution values.
-   * @return {(String|Function)}                - Either an intermediary tag function or the results of processing the template.
+   * @param  {(Function|String|Array<String>)} strings        - Either a template tag or an array containing template strings separated by identifier
+   * @param  {...*}                            ...expressions - Optional list of substitution values.
+   * @return {(String|Function)}                              - Either an intermediary tag function or the results of processing the template.
    */
-  tag = (...args) => {
-    // if the first argument passed is a function, assume it is a template tag and return
-    // an intermediary tag that processes the template using the aforementioned tag, passing the
-    // result to our tag
-    if (typeof args[0] === 'function') {
-      return this.interimTag.bind(this, args.shift())
+  tag = (strings, ...expressions) => {
+    if (typeof strings === 'function') {
+      // if the first argument passed is a function, assume it is a template tag and return
+      // an intermediary tag that processes the template using the aforementioned tag, passing the
+      // result to our tag
+      return this.interimTag.bind(this, strings)
+    }
+
+    if (typeof strings === 'string') {
+      // if the first argument passed is a string, just transform it
+      return this.transformEndResult(strings)
     }
 
     // else, return a transformed end result of processing the template with our tag
     return this.transformEndResult(
-      args.shift().reduce(this.processSubstitutions.bind(this, args))
+      strings.reduce(this.processSubstitutions.bind(this, expressions))
     )
   }
 

src/TemplateTag/TemplateTag.test.js

@@ -89,3 +89,21 @@ test('supports tail processing of another tag if first argument to tag is a tag'
   `
   t.is(raw, 'FOO BAR\n    500')
 })
+
+test('supports passing string as a first argument', (t) => {
+  let onSubstitutionCalls = 0
+  const tag = new TemplateTag({
+    onSubstitution () {
+      onSubstitutionCalls += 1
+    },
+    onEndResult (endResult) {
+      return endResult.toUpperCase().trim()
+    }
+  })
+  const raw = tag(`
+    foo bar
+    ${500}
+  `)
+  t.is(raw, 'FOO BAR\n    500')
+  t.is(onSubstitutionCalls, 0, 'The `onSubstitution` hook shouldn\'t be called')
+})