feat!: Use const and => notation for function stringification

BREAKING CHANGE: While using ES6 syntax for functions does not change
their behaviour in any way, it will need to be transpiled if the target
environment (e.g. IE 11) does not support it.

packages/cli/src/print-plurals.js

@@ -26,13 +26,11 @@ export default function printPluralsModule(args) {
   const plurals = []
   for (const [fn, locales] of Object.entries(localesByFn)) {
     if (locales.length > maxRepeat && commonId <= 'z') {
-      str += fn.replace(/^function\b/, `function ${commonId}`) + '\n'
+      str += `const ${commonId} = ${fn};\n`
       for (const lc of locales) plurals.push({ lc, id: commonId })
       commonId = String.fromCharCode(commonId.charCodeAt(0) + 1)
     } else {
-      for (const lc of locales) {
-        plurals.push({ lc, fn: fn.replace(/^function\b/, `function ${lc}`) })
-      }
+      for (const lc of locales) plurals.push({ lc, fn })
     }
   }
   plurals.sort((a, b) => (a.lc < b.lc ? -1 : 1))
@@ -42,10 +40,8 @@ export default function printPluralsModule(args) {
     const pm = plurals.map(({ lc, id, fn }) => `${lc}: ${id || fn}`)
     str += printUMD('plurals', pm.join(',\n\n')) + '\n'
   } else {
-    for (const { lc, id, fn } of plurals) {
-      if (id) str += `export const ${lc} = ${id};\n`
-      else str += `export ${fn}\n`
-    }
+    for (const { lc, id, fn } of plurals)
+      str += `export const ${lc} = ${id || fn};\n`
   }
   return str
 }

packages/cli/src/print-types.js

@@ -36,7 +36,7 @@ export default function printPluralTypes(args) {
     mpc.test()
     const id = identifier(lc)
     const cat = stringifyCategories(args, mpc.categories)
-    str += `export function ${id}(${fnArgs}): ${cat};\n`
+    str += `export const ${id}: (${fnArgs}) => ${cat};\n`
   }
   return str
 }

packages/compiler/src/compiler.js

@@ -42,16 +42,16 @@ export default class Compiler {
   compile() {
     if (!this.fn) {
       this.fn = this.buildFunction()
-      this.fn.toString = name => {
-        const str = Function.prototype.toString.call(this.fn)
-        const func = name ? `function ${name}` : 'function'
+      this.fn.toString = () =>
         // The /*``*/ is present in Node 8 output, due to
         // https://bugs.chromium.org/p/v8/issues/detail?id=2470
-        return str.replace(
-          /^function(?: \w+)\(([^)]+)\)/,
-          (_, args) => `${func}(${args.replace('/*``*/', '').trim()})`
-        )
-      }
+        Function.prototype.toString
+          .call(this.fn)
+          .replace(
+            /^function(?: \w+)\(([^)]+)\)/,
+            (_, args) => `(${args.replace('/*``*/', '').trim()}) =>`
+          )
+          .replace(/{\s*return\s+([^{}]*);\s*}$/, '$1')
       this.test = () => this.tests.testAll(this.fn)
     }
     return this.fn

packages/compiler/src/parser.js

@@ -62,6 +62,6 @@ export default class Parser {
       }
     }
     if (!vars.length) return ''
-    return 'var ' + ["s = String(n).split('.')", ...vars].join(', ')
+    return 'const ' + ["s = String(n).split('.')", ...vars].join(', ')
   }
 }