limitTo.js

'use strict';

/**
 * @ngdoc filter
 * @name limitTo
 * @kind function
 *
 * @description
 * Creates a new array or string containing only a specified number of elements. The elements
 * are taken from either the beginning or the end of the source array, string or number, as specified by
 * the value and sign (positive or negative) of `limit`. If a number is used as input, it is
 * converted to a string.
 *
 * @param {Array|string|number} input Source array, string or number to be limited.
 * @param {string|number} limit The length of the returned array or string. If the `limit` number
 *     is positive, `limit` number of items from the beginning of the source array/string are copied.
 *     If the number is negative, `limit` number  of items from the end of the source array/string
 *     are copied. The `limit` will be trimmed if it exceeds `array.length`. If `limit` is undefined,
 *     the input will be returned unchanged.
 * @param {string|number} begin Index at which to begin limitation. As a negative index, `begin`
 *     indicates an offset from the end of `input`. Defaults to `0`.
 * @returns {Array|string} A new sub-array or substring of length `limit` or less if input array
 *     had less than `limit` elements.
 *
 * @example
   <example module="limitToExample">
     <file name="index.html">
       <script>
         angular.module('limitToExample', [])
           .controller('ExampleController', ['$scope', function($scope) {
             $scope.numbers = [1,2,3,4,5,6,7,8,9];
             $scope.letters = "abcdefghi";
             $scope.longNumber = 2345432342;
             $scope.numLimit = 3;
             $scope.letterLimit = 3;
             $scope.longNumberLimit = 3;
           }]);
       </script>
       <div ng-controller="ExampleController">
         Limit {{numbers}} to: <input type="number" step="1" ng-model="numLimit">
         <p>Output numbers: {{ numbers | limitTo:numLimit }}</p>
         Limit {{letters}} to: <input type="number" step="1" ng-model="letterLimit">
         <p>Output letters: {{ letters | limitTo:letterLimit }}</p>
         Limit {{longNumber}} to: <input type="number" step="1" ng-model="longNumberLimit">
         <p>Output long number: {{ longNumber | limitTo:longNumberLimit }}</p>
       </div>
     </file>
     <file name="protractor.js" type="protractor">
       var numLimitInput = element(by.model('numLimit'));
       var letterLimitInput = element(by.model('letterLimit'));
       var longNumberLimitInput = element(by.model('longNumberLimit'));
       var limitedNumbers = element(by.binding('numbers | limitTo:numLimit'));
       var limitedLetters = element(by.binding('letters | limitTo:letterLimit'));
       var limitedLongNumber = element(by.binding('longNumber | limitTo:longNumberLimit'));

       it('should limit the number array to first three items', function() {
         expect(numLimitInput.getAttribute('value')).toBe('3');
         expect(letterLimitInput.getAttribute('value')).toBe('3');
         expect(longNumberLimitInput.getAttribute('value')).toBe('3');
         expect(limitedNumbers.getText()).toEqual('Output numbers: [1,2,3]');
         expect(limitedLetters.getText()).toEqual('Output letters: abc');
         expect(limitedLongNumber.getText()).toEqual('Output long number: 234');
       });

       // There is a bug in safari and protractor that doesn't like the minus key
       // it('should update the output when -3 is entered', function() {
       //   numLimitInput.clear();
       //   numLimitInput.sendKeys('-3');
       //   letterLimitInput.clear();
       //   letterLimitInput.sendKeys('-3');
       //   longNumberLimitInput.clear();
       //   longNumberLimitInput.sendKeys('-3');
       //   expect(limitedNumbers.getText()).toEqual('Output numbers: [7,8,9]');
       //   expect(limitedLetters.getText()).toEqual('Output letters: ghi');
       //   expect(limitedLongNumber.getText()).toEqual('Output long number: 342');
       // });

       it('should not exceed the maximum size of input array', function() {
         numLimitInput.clear();
         numLimitInput.sendKeys('100');
         letterLimitInput.clear();
         letterLimitInput.sendKeys('100');
         longNumberLimitInput.clear();
         longNumberLimitInput.sendKeys('100');
         expect(limitedNumbers.getText()).toEqual('Output numbers: [1,2,3,4,5,6,7,8,9]');
         expect(limitedLetters.getText()).toEqual('Output letters: abcdefghi');
         expect(limitedLongNumber.getText()).toEqual('Output long number: 2345432342');
       });
     </file>
   </example>
*/
function limitToFilter() {
  return function(input, limit, begin) {
    if (Math.abs(Number(limit)) === Infinity) {
      limit = Number(limit);
    } else {
      limit = toInt(limit);
    }
    if (isNaN(limit)) return input;

    if (isNumber(input)) input = input.toString();
    if (!isArray(input) && !isString(input)) return input;

    begin = (!begin || isNaN(begin)) ? 0 : toInt(begin);
    begin = (begin < 0 && begin >= -input.length) ? input.length + begin : begin;

    if (limit >= 0) {
      return input.slice(begin, begin + limit);
    } else {
      if (begin === 0) {
        return input.slice(limit, input.length);
      } else {
        return input.slice(Math.max(0, begin + limit), begin);
      }
    }
  };
}