[Fix] reduce/reduceRight: follow Array#reduce when omitting initialValue

docs/api/ReactWrapper/reduce.md

@@ -12,8 +12,7 @@ following arguments:
   - `node` (`ReactWrapper`): A wrapper around the current node being processed
   - `index` (`Number`): The index of the current node being processed
 
-2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the
-first invocation of the reducing function.
+2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the first invocation of the reducing function. If omitted, the first `node` will be provided and the iteration will begin on the second node in the collection.
 
 
 

docs/api/ReactWrapper/reduceRight.md

@@ -12,8 +12,7 @@ following arguments:
   - `node` (`ReactWrapper`): A wrapper around the current node being processed
   - `index` (`Number`): The index of the current node being processed
 
-2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the
-first invocation of the reducing function.
+2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the first invocation of the reducing function. If omitted, the first `node` will be provided and the iteration will begin on the second node in the collection.
 
 
 

docs/api/ShallowWrapper/reduce.md

@@ -12,8 +12,7 @@ following arguments:
   - `node` (`ShallowWrapper`): A wrapper around the current node being processed
   - `index` (`Number`): The index of the current node being processed
 
-2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the
-first invocation of the reducing function.
+2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the first invocation of the reducing function. If omitted, the first `node` will be provided and the iteration will begin on the second node in the collection.
 
 
 

docs/api/ShallowWrapper/reduceRight.md

@@ -12,8 +12,7 @@ following arguments:
   - `node` (`ShallowWrapper`): A wrapper around the current node being processed
   - `index` (`Number`): The index of the current node being processed
 
-2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the
-first invocation of the reducing function.
+2. `initialValue` (`T` [optional]): If provided, this will be passed in as the first argument to the first invocation of the reducing function. If omitted, the first `node` will be provided and the iteration will begin on the second node in the collection.
 
 
 

packages/enzyme-test-suite/test/ReactWrapper-spec.jsx

@@ -21,6 +21,9 @@ import {
 import { ITERATOR_SYMBOL, sym } from 'enzyme/build/Utils';
 import { REACT013, REACT014, REACT16, is } from './_helpers/version';
 
+const getElementPropSelector = prop => x => x.props[prop];
+const getWrapperPropSelector = prop => x => x.prop(prop);
+
 describeWithDOM('mount', () => {
   describe('top level wrapper', () => {
     it('does what i expect', () => {
@@ -2348,6 +2351,10 @@ describeWithDOM('mount', () => {
   });
 
   describe('.reduce(fn[, initialValue])', () => {
+    it('has the right length', () => {
+      expect(ReactWrapper.prototype.reduce).to.have.lengthOf(1);
+    });
+
     it('should call a function with a wrapper for each node in the wrapper', () => {
       const wrapper = mount(
         <div>
@@ -2388,9 +2395,33 @@ describeWithDOM('mount', () => {
         baz: 'foo hoo',
       });
     });
+
+    it('allows the initialValue to be omitted', () => {
+      const one = (<div id="bax" className="foo qoo" />);
+      const two = (<div id="bar" className="foo boo" />);
+      const three = (<div id="baz" className="foo hoo" />);
+      const wrapper = mount(
+        <div>
+          {one}
+          {two}
+          {three}
+        </div>,
+      );
+      const counter = (<noscript id="counter" />);
+      const result = wrapper
+        .find('.foo')
+        .reduce((acc, n) => [].concat(acc, n, new ReactWrapper(counter)))
+        .map(getWrapperPropSelector('id'));
+
+      expect(result).to.eql([one, two, counter, three, counter].map(getElementPropSelector('id')));
+    });
   });
 
   describe('.reduceRight(fn[, initialValue])', () => {
+    it('has the right length', () => {
+      expect(ReactWrapper.prototype.reduceRight).to.have.lengthOf(1);
+    });
+
     it('should call a function with a wrapper for each node in the wrapper in reverse', () => {
       const wrapper = mount(
         <div>
@@ -2431,6 +2462,27 @@ describeWithDOM('mount', () => {
         baz: 'foo hoo',
       });
     });
+
+    it('allows the initialValue to be omitted', () => {
+      const one = (<div id="bax" className="foo qoo" />);
+      const two = (<div id="bar" className="foo boo" />);
+      const three = (<div id="baz" className="foo hoo" />);
+      const wrapper = mount(
+        <div>
+          {one}
+          {two}
+          {three}
+        </div>,
+      );
+
+      const counter = (<noscript id="counter" />);
+      const result = wrapper
+        .find('.foo')
+        .reduceRight((acc, n) => [].concat(acc, n, new ReactWrapper(counter)))
+        .map(getWrapperPropSelector('id'));
+
+      expect(result).to.eql([three, two, counter, one, counter].map(getElementPropSelector('id')));
+    });
   });
 
   describe('.slice([begin[, end]])', () => {

packages/enzyme-test-suite/test/ShallowWrapper-spec.jsx

@@ -14,6 +14,9 @@ import { REACT013, REACT014, REACT16, is } from './_helpers/version';
 // we should be able to go un-skip all of the tests that are skipped with this flag.
 const BATCHING = !REACT16;
 
+const getElementPropSelector = prop => x => x.props[prop];
+const getWrapperPropSelector = prop => x => x.prop(prop);
+
 describe('shallow', () => {
   describe('top level wrapper', () => {
     it('does what i expect', () => {
@@ -2131,6 +2134,10 @@ describe('shallow', () => {
   });
 
   describe('.reduce(fn[, initialValue])', () => {
+    it('has the right length', () => {
+      expect(ShallowWrapper.prototype.reduce).to.have.lengthOf(1);
+    });
+
     it('should call a function with a wrapper for each node in the wrapper', () => {
       const wrapper = shallow(
         <div>
@@ -2174,9 +2181,33 @@ describe('shallow', () => {
         baz: 'foo hoo',
       });
     });
+
+    it('allows the initialValue to be omitted', () => {
+      const one = (<div id="bax" className="foo qoo" />);
+      const two = (<div id="bar" className="foo boo" />);
+      const three = (<div id="baz" className="foo hoo" />);
+      const wrapper = shallow(
+        <div>
+          {one}
+          {two}
+          {three}
+        </div>,
+      );
+      const counter = (<noscript id="counter" />);
+      const result = wrapper
+        .find('.foo')
+        .reduce((acc, n) => [].concat(acc, n, new ShallowWrapper(counter)))
+        .map(getWrapperPropSelector('id'));
+
+      expect(result).to.eql([one, two, counter, three, counter].map(getElementPropSelector('id')));
+    });
   });
 
   describe('.reduceRight(fn[, initialValue])', () => {
+    it('has the right length', () => {
+      expect(ShallowWrapper.prototype.reduceRight).to.have.lengthOf(1);
+    });
+
     it('should call a function with a wrapper for each node in the wrapper in reverse', () => {
       const wrapper = shallow(
         <div>
@@ -2220,6 +2251,26 @@ describe('shallow', () => {
         baz: 'foo hoo',
       });
     });
+
+    it('allows the initialValue to be omitted', () => {
+      const one = (<div id="bax" className="foo qoo" />);
+      const two = (<div id="bar" className="foo boo" />);
+      const three = (<div id="baz" className="foo hoo" />);
+      const wrapper = shallow(
+        <div>
+          {one}
+          {two}
+          {three}
+        </div>,
+      );
+      const counter = (<noscript id="counter" />);
+      const result = wrapper
+        .find('.foo')
+        .reduceRight((acc, n) => [].concat(acc, n, new ShallowWrapper(counter)))
+        .map(getWrapperPropSelector('id'));
+
+      expect(result).to.eql([three, two, counter, one, counter].map(getElementPropSelector('id')));
+    });
   });
 
   describe('.slice([begin[, end]])', () => {

packages/enzyme/src/ReactWrapper.js

@@ -783,11 +783,19 @@ class ReactWrapper {
    * @param {*} initialValue - the initial value
    * @returns {*}
    */
-  reduce(fn, initialValue) {
-    return this.getNodesInternal().reduce(
-      (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
-      initialValue,
-    );
+  reduce(fn, initialValue = undefined) {
+    if (arguments.length > 1) {
+      return this.getNodesInternal().reduce(
+        (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
+        initialValue,
+      );
+    }
+    return this.getNodesInternal().reduce((accum, n, i) => fn.call(
+      this,
+      i === 1 ? this.wrap(accum) : accum,
+      this.wrap(n),
+      i,
+    ));
   }
 
   /**
@@ -798,11 +806,19 @@ class ReactWrapper {
    * @param {*} initialValue - the initial value
    * @returns {*}
    */
-  reduceRight(fn, initialValue) {
-    return this.getNodesInternal().reduceRight(
-      (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
-      initialValue,
-    );
+  reduceRight(fn, initialValue = undefined) {
+    if (arguments.length > 1) {
+      return this.getNodesInternal().reduceRight(
+        (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
+        initialValue,
+      );
+    }
+    return this.getNodesInternal().reduceRight((accum, n, i) => fn.call(
+      this,
+      i === 1 ? this.wrap(accum) : accum,
+      this.wrap(n),
+      i,
+    ));
   }
 
   /**

packages/enzyme/src/ShallowWrapper.js

@@ -892,11 +892,19 @@ class ShallowWrapper {
    * @param {*} initialValue - the initial value
    * @returns {*}
    */
-  reduce(fn, initialValue) {
-    return this.getNodesInternal().reduce(
-      (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
-      initialValue,
-    );
+  reduce(fn, initialValue = undefined) {
+    if (arguments.length > 1) {
+      return this.getNodesInternal().reduce(
+        (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
+        initialValue,
+      );
+    }
+    return this.getNodesInternal().reduce((accum, n, i) => fn.call(
+      this,
+      i === 1 ? this.wrap(accum) : accum,
+      this.wrap(n),
+      i,
+    ));
   }
 
   /**
@@ -907,11 +915,19 @@ class ShallowWrapper {
    * @param {*} initialValue - the initial value
    * @returns {*}
    */
-  reduceRight(fn, initialValue) {
-    return this.getNodesInternal().reduceRight(
-      (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
-      initialValue,
-    );
+  reduceRight(fn, initialValue = undefined) {
+    if (arguments.length > 1) {
+      return this.getNodesInternal().reduceRight(
+        (accum, n, i) => fn.call(this, accum, this.wrap(n), i),
+        initialValue,
+      );
+    }
+    return this.getNodesInternal().reduceRight((accum, n, i) => fn.call(
+      this,
+      i === 1 ? this.wrap(accum) : accum,
+      this.wrap(n),
+      i,
+    ));
   }
 
   /**