多维数组降维的几种方法

    var a = [1,2,[3,4]]
    var result = [];
    for(var i=0; i< a.length; i++){
        if(a[i].constructor == Array) {
            for(var j=0; j<a[i].length; j++){
                result.push(a[i][j])
            }
        }else {
            result.push(a[i])
        }
    }
    console.log(result)// [1,2,3,4]

    var a = [1,2,[3,4]]
    var result = []
    for(var i=0; i<a.length; i++){
        if(a[i].constructor == Array) {
            result = result.concat(a[i])
        }else {
            result.push(a[i])
        }
    }
    console.log(result) // [1,2,3,4]

    var a = [1,2,[3,4]]
    var result = []
    result = [].concat(...a)
    console.log(result) // [1,2,3,4]

　　　var a = [1,2,[3,4]]
     var result = []
     result = Array.prototype.concat.apply([], a)
     console.log(result) // [1,2,3,4]