feat(StringWrapper): add support for JS slice method to string

Author: itslenny

modules/angular2/src/core/facade/lang.dart

@@ -94,6 +94,14 @@ class StringWrapper {
  return s.startsWith(start);
  }
 
+ static String slice(String s, [int start = 0, int end]) {
+ //in JS if start > end an empty string is returned
+ if(end != null && start > end) {
+ return "";
+ }
+ return s.substring(_startOffset(s, start), _endOffset(s, end));
+ }
+
  static String substring(String s, int start, [int end]) {
  return s.substring(start, end);
  }
@@ -107,6 +115,21 @@ class StringWrapper {
  }
 
  static int compare(String a, String b) => a.compareTo(b);
+
+ // JS slice function can take start < 0 which indicates a position relative to
+ // the end of the string
+ static int _startOffset(String s, int start) {
+ int len = s.length;
+ return start = start < 0 ? math.max(len + start, 0) : math.min(start, len);
+ }
+
+ // JS slice function can take end < 0 which indicates a position relative to
+ // the end of the string
+ static int _endOffset(String s, int end) {
+ int len = s.length;
+ if (end == null) return len;
+ return end < 0 ? math.max(len + end, 0) : math.min(end, len);
+ }
 }
 
 class StringJoiner {

modules/angular2/src/core/facade/lang.ts

@@ -151,6 +151,10 @@ export class StringWrapper {
  return s.replace(from, replace);
  }
 
+ static slice<T>(s: string, from: number = 0, to: number = null): string {
+ return s.slice(from, to === null ? undefined : to);
+ }
+
  static toUpperCase(s: string): string { return s.toUpperCase(); }
 
  static toLowerCase(s: string): string { return s.toLowerCase(); }

modules/angular2/test/core/facade/lang_spec.ts

@@ -42,7 +42,7 @@ export function main() {
  });
 
  describe('String', () => {
- var upper, lower;
+ var upper, lower, s;
 
  beforeEach(() => {
  upper = 'SOMETHING';
@@ -60,5 +60,25 @@ export function main() {
 
  expect(str).toEqual(lower);
  });
+
+ describe('slice', () => {
+ beforeEach(() => { s = "abcdefghij"; });
+
+ it('should return the whole string if neither start nor end are specified',
+ () => { expect(StringWrapper.slice(s)).toEqual("abcdefghij"); });
+
+ it('should return up to the end if end is not specified',
+ () => { expect(StringWrapper.slice(s, 1)).toEqual("bcdefghij"); });
+
+ it('should support negative start',
+ () => { expect(StringWrapper.slice(s, -1)).toEqual("j"); });
+
+ it('should support negative end',
+ () => { expect(StringWrapper.slice(s, -3, -1)).toEqual("hi"); });
+
+ it('should return empty string if start is greater than end',
+ () => { expect(StringWrapper.slice(s, 4, 2)).toEqual(""); });
+ });
+
  });
 }