将每个对象中的字符串循环到一个字符串

Question

如何将每个对象中的循环字符串添加到一个字符串中，如下所示？
我需要将每个变量this_encode 添加到一个字符串中，怎么做？

result: '<img src=""><iframe></iframe><img src="">'

for (var key in obj) {
    if (obj[key].file_type == 0) {
        var this_encode = '<img src="' + obj[key].file_name + obj[key].file_format + '">';
    } else if(obj[key].file_type == 1) {
        var this_encode = '<iframe width="150" height="100" src="'+obj[key].file_embed_url +'" frameborder="0" allowfullscreen></iframe>';
    }
}

对象

file_embed_url: ""  
file_format: "jpg"  
file_name: "53b21c90dded9"  
file_sequence: "0"  
file_type: "0"  
gallery_id: "1"  
id: "138"  

file_embed_url: "//www.youtube.com/embed/-x6jzKpqeuw"  
file_format: ""  
file_name: ""  
file_sequence: "1"  
file_type: "1"  
gallery_id: "1"  
id: "139"  

...

Answer 1

在循环外声明this_encode 变量，然后使用连接创建单个字符串

// first initialise your variable as an empty string; can't concatenate to undefined
var this_encode = '';

// Now run your code as before with 2 small differences
//      (1) Remove the var declarations
//      (2) Use += instead of = to indicate that you want to append the following text to the this_encode variable
for (var key in obj) {
    if (obj[key].file_type == 0) {
        this_encode += '<img src="' + obj[key].file_name + obj[key].file_format + '">';
    //  ^           ^ see the change here
    //  |
    //  var declartion removed from here (and below)
    } else if(obj[key].file_type == 1) {
        this_encode += '<iframe width="150" height="100" src="'+obj[key].file_embed_url +'" frameborder="0" allowfullscreen></iframe>';
        //          ^ and here
    }
}