这段代码在javascript中是什么意思

Question

 var sb = document.getElementById("top_search_box");
        var val = sb.value;
        if(!val) val = "";
        val = val.replace(/^[ ]+/g, "").replace(/[ ]+$/g, "");
        if(val == "" || val=="Search for Items") {
            sb.focus();
            return false;
        }
        return true;

Answer 1

它消除了一个元素中的空值或该值中的尾随空格（可能是文本输入），如果它包含默认值或空值，则将其聚焦。

Answer 2

This code checks to see if the search box has user-inputted value. If it does, it returns true. If it doesn't, it focuses on the search box (places the cursor in there) and returns false. Due to the fact that there are return statements, I'm guessing this is code from a function.

var sb = document.getElementById("top_search_box");

The above code gets the search box, and puts a reference to it in the variable sb

var val = sb.value;

This gets the value of the search box, and puts it in the variable val

if(!val) val = "";

If val is not set, this sets it to the empty string

val = val.replace(/^[ ]+/g, "").replace(/[ ]+$/g, "");

This trims any spaces off the beginning and end of val , so all that's left is the actual value, if there is one, or an empty string if it was only spaces.

if(val == "" || val=="Search for Items") {
    sb.focus();
    return false;
}

If, after all of this, val holds the empty string, or the (presumably default) string "Search for Items", the cursor is moved to the search box, and the function returns false.

return true;

Otherwise, the function returns true.

In the end, it seems the function returns true if there is a user inputted value, and false otherwise. This could be useful if you need to know if a user has put anything in the search box.

Answer 3

该代码检查ID = top_search_box的输入字段是否具有任何值，如果没有，则将输入字段的值更新为“搜索项目”

Answer 4

val = val.replace(/^[ ]+/g, "").replace(/[ ]+$/g, "");

Remove spaces from start and end of value from the top search box

rest of are very simple.