参考了一下答案,之前没写var j=0和j=j+1

var infos = 

 [

  ['小A','女',21,'大一'],

['小B','男',23,'大三'],

['小C','男',24,'大四'],

['小D','女',21,'大一'],

['小E','女',22,'大四'],

  ['小F','男',21,'大一'],

['小G','女',22,'大二'],

['小H','女',20,'大三'],

['小I','女',20,'大一'],

['小J','男',20,'大三']

  ];

var myarr=[];

var j=0

for(var i = 0, length1 = infos.length; i < length1; i++){

if(infos[i][3]=='大一'){

myarr[j]=infos[i];

j=j+1;

}

}

for(var j = 0, length2 = myarr.length; j < length2; j++){

if(myarr[j][1]=='女'){

document.write(myarr[j][0]);

}

}

请教,为什么要写var j=0和j=j+1呢?