feat(result): values of default params to be always strings (#121)

Changes in [Result object](https://github.com/tunnckoCore/parse-function#result)!

**Possible breaking change, if you depend on values of `result.defaults`!**

Now `result.defaults` is key/value pairs as before, but the value is always of type `string` or `undefined`!
Casting of values is delegated to the end user which before was not consistent and was actual value of the default parameter.

Example **(before)**:

```js
const result = app.parse('(a = 123) => {}')
console.log(result.defaults)
// => { a: 123 }
```

Example **(after)**:

```js
const result = app.parse('(a = 123) => {}')

// notice that `123` now is string!
console.log(result.defaults)
// => { a: '123' }
```

fixes #120, related #110

Author: Eric MORAND

src/lib/plugins/params.js

@@ -34,16 +34,12 @@ export default (app) => (node, result) => {
     result.args.push(name)
 
     if (param.right && param.right.type === 'SequenceExpression') {
-      let value
       let lastExpression = param.right.expressions.pop()
 
-      if (lastExpression.type === 'NullLiteral') {
-        value = null
-      } else {
-        value = lastExpression.value
-      }
-
-      result.defaults[name] = value
+      result.defaults[name] = result.value.slice(
+        lastExpression.start,
+        lastExpression.end
+      )
     } else {
       result.defaults[name] = param.right
         ? result.value.slice(param.right.start, param.right.end)

test/index.js

@@ -31,7 +31,9 @@ const actuals = {
     'function () {}',
     'function (a = (true, false)) {}',
     'function (a = (true, null)) {}',
+    'function (a = (true, "bar")) {}',
     'function (a, b = (i++, true)) {}',
+    'function (a = 1) {}',
   ],
   named: [
     'function namedFn (a = {foo: "ba)r", baz: 123}, cb, ...restArgs) {return a * 3}',
@@ -41,7 +43,9 @@ const actuals = {
     'function namedFn () {}',
     'function namedFn(a = (true, false)) {}',
     'function namedFn(a = (true, null)) {}',
+    'function namedFn(a = (true, "bar")) {}',
     'function namedFn(a, b = (i++, true)) {}',
+    'function namedFn(a = 1) {}',
   ],
   generators: [
     'function * namedFn (a = {foo: "ba)r", baz: 123}, cb, ...restArgs) {return a * 3}',
@@ -51,7 +55,9 @@ const actuals = {
     'function * namedFn () {}',
     'function * namedFn(a = (true, false)) {}',
     'function * namedFn(a = (true, null)) {}',
+    'function * namedFn(a = (true, "bar")) {}',
     'function * namedFn(a, b = (i++, true)) {}',
+    'function * namedFn(a = 1) {}',
   ],
   arrows: [
     '(a = {foo: "ba)r", baz: 123}, cb, ...restArgs) => {return a * 3}',
@@ -61,7 +67,9 @@ const actuals = {
     '() => {}',
     '(a = (true, false)) => {}',
     '(a = (true, null)) => {}',
+    '(a = (true, "bar")) => {}',
     '(a, b = (i++, true)) => {}',
+    '(a = 1) => {}',
     '(a) => a * 3 * a',
     'd => d * 355 * d',
     'e => {return e + 5235 / e}',
@@ -126,21 +134,35 @@ const regulars = [
     params: 'a',
     args: ['a'],
     body: '',
-    defaults: {a: false},
+    defaults: { a: 'false' },
   },
   {
     name: null,
     params: 'a',
     args: ['a'],
     body: '',
-    defaults: {a: null},
+    defaults: { a: 'null' },
+  },
+  {
+    name: null,
+    params: 'a',
+    args: ['a'],
+    body: '',
+    defaults: { a: '"bar"' },
   },
   {
     name: null,
     params: 'a, b',
     args: ['a', 'b'],
     body: '',
-    defaults: {a: undefined, b: true},
+    defaults: { a: undefined, b: 'true' },
+  },
+  {
+    name: null,
+    params: 'a',
+    args: ['a'],
+    body: '',
+    defaults: { a: '1' },
   },
 ]