数组-不修改原数组

  • arr.slice( begin[, end] )
    var students = [
    {id: 1, score: 80},
    {id: 2, score: 50},
    {id: 3, score: 70}
    ];
    var newStudents = students.slice(0, 2);
    /*
    [
    {id: 1, score: 80},
    {id: 2, score: 50}
    ];
    */
  • arr.concat( value1, ..., valueN )
    var students1 = [
    {id: 1, score: 80},
    {id: 2, score: 50},
    {id: 3, score: 70}
    ];
    var students2 = [
    {id: 4, score: 90},
    {id: 5, score: 60}
    ];
    var students3 = [
    {id: 6, score: 40},
    {id: 7, score: 30}
    ];
    var newStudents = students1.concat(students2, students3);
    /*
    [
    {id: 1, score: 80},
    {id: 2, score: 50},
    {id: 3, score: 70},
    {id: 4, score: 90},
    {id: 5, score: 60},
    {id: 6, score: 40},
    {id: 7, score: 30}
    ];
    */
  • arr.join( [separator] )
    var emails = ["wq@163.com","gp@163.com","xl@163.com"];
    emails.join(";"); // => "wq@163.com;gp@163.com;xl@163.com"
  • arr.map( callback[, thisArg] )
    var scores = [60,70,80,90];
    var addScore = function (item, index, array) {
    return item + 5;
    }
    var newScores = scores.map(addScore); // => [65,75,85,95]
  • arr.reduce(callback[, initialValue])
    var students = [
    {id: 1, score: 80},
    {id: 2, score: 50},
    {id: 3, score: 70}
    ];
    var sum = function(previousResult, item, index, array) {
    return preiousResult + item.score;
    };
    students.reduce(sum, 0); // => 200
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