数组-修改原数组

• arr.indexOf( searchElement[, formindex=0] )
  var telephones = [110,120,114];
  telephones.indexOf(120); // => 1
  telephones.indexOf(119); // => -1
• arr.forEach( callback[, thisArg] )
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  var editScore = function (item, index, array) {
  item.score += 5;
  };
  students.forEach(editScore);
  students[0].score; // => 85
• arr.reverse()
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.reverse();
  students[0].score; // => 70
• arr.sort( [compareFunction] )
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  var byScore = function (a, b) {
  return b.score - a.score;
  }
  /*
  [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  */
• arr.push( element1, ..., elementN )
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.push({id: 4, score: 90});
  /*
  [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70},
  {id: 4, score: 90}
  ];
  */
• arr.unshift( element1, ..., elementN )
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.unshift({id: 4, score: 90});
  /*
  [
  {id: 4, score: 90}
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  */
• arr.shift()
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.shift();
  /*
  [
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  */
• arr.pop()
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.pop();
  /*
  [
  {id: 1, score: 80},
  {id: 2, score: 50}
  ];
  */
• srr.splice( index, howMany[, ele1[, ...[, eleN]]] )
  var students = [
  {id: 1, score: 80},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  students.splice(1, 1, {id: 4, score: 90});
  /*
  [
  {id: 1, score: 80},
  {id: 4, score: 90},
  {id: 3, score: 70}
  ];
  /
  students.splice(1, 0, {id: 4, score: 90});
  /
  [
  {id: 1, score: 80},
  {id: 4, score: 90},
  {id: 2, score: 50},
  {id: 3, score: 70}
  ];
  /
  students.splice(1, 1);
  /
  [
  {id: 1, score: 80},
  {id: 3, score: 70}
  ];
  */