fix: link's title should not to be string (#7)

[link](http://example.com "title")

should be

link

Author: azu

src/StringSource.js

@@ -151,12 +151,22 @@ export default class StringSource {
         return node.type === "Str";
     }
 
+    /**
+     *
+     * @param node
+     * @returns {string|undefined}
+     * @private
+     */
     _getValue(node) {
         if (node.value) {
             return node.value;
         } else if (node.alt) {
             return node.alt;
         } else if (node.title) {
+            // See https://github.com/azu/textlint-rule-sentence-length/issues/6
+            if (node.type === "Link") {
+                return;
+            }
             return node.title;
         }
     }
@@ -178,11 +188,11 @@ export default class StringSource {
         // [padding][value][padding]
         // =>
         // [value][value][value]
-        let value = this._getValue(node);
+        const value = this._getValue(node);
         if (!value) {
             return;
         }
-        if (parent == null) {
+        if (parent === null || parent === undefined) {
             return;
         }
         // <p><Str /></p>

test/StringSource-test.js

@@ -95,6 +95,27 @@ describe("StringSource", function() {
                 value: "link"
             });
         });
+
+        it("Link's title should be ignored", function() {
+            let AST = parse('_[link](http://example "title")');
+            let source = new StringSource(AST);
+            let result = source.toString();
+            assert.equal(result, "_link");
+            let tokenStr = source.tokenMaps[0];
+            assert.deepEqual(tokenStr, {
+                generated: [0, 1],
+                intermediate: [0, 1],
+                original: [0, 1],
+                value: "_"
+            });
+            let tokenLink = source.tokenMaps[1];
+            assert.deepEqual(tokenLink, {
+                generated: [1, 5],
+                intermediate: [2, 6],
+                original: [1, 31],
+                value: "link"
+            });
+        });
         it("Str + `Code` + Str", function() {
             let AST = parse("text`code`text");
             let source = new StringSource(AST);
@@ -152,6 +173,25 @@ describe("StringSource", function() {
                 value: " text"
             });
         });
+        it("Image's title should be ignored", function() {
+            let AST = parse('![alt](http://example.png "title") text');
+            let source = new StringSource(AST);
+            let result = source.toString();
+            assert.equal(result, "alt text");
+            assert.equal(source.tokenMaps.length, 2);
+            assert.deepEqual(source.tokenMaps[0], {
+                generated: [0, 3],
+                intermediate: [2, 5],
+                original: [0, 34],
+                value: "alt"
+            });
+            assert.deepEqual(source.tokenMaps[1], {
+                generated: [3, 8],
+                intermediate: [34, 39],
+                original: [34, 39],
+                value: " text"
+            });
+        });
         it("confusing pattern", function() {
             let AST = parse("![!](http://example.com)");
             let source = new StringSource(AST);