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Introduction to how to write a simple and efficient JSON query using function templates_javascript skills

WBOYOriginal: 2016-05-16 17:36:40887browse

JSON can be said to be the highlight of JavaScript. It can implement the initialization of Object and Array with elegant and concise code. It is also a text-based data definition, which is more semantic than symbol separation and more concise than XML. Therefore, more and more JS developers use it as data transmission and storage.

JS arrays have many useful methods built-in to facilitate our query and filtering of data. For example, we have a bunch of data:

Copy code The code is as follows:

var heroes = [
          // Name============Attack======Defense========Strength====Dexterity=====Intelligence====
                                                         name: 'Ice Room Witch', DP: 38, AP: 1.3, STR: 16, AGI: 16, int: 21}, 
 {name: 'Silent Warlock', DP: 39, AP: 1.1, STR: 17, Agi:16, Int:21},
 {name:'Naga Siren', DP:51, AP:6.0, Str:21, Agi:21, Int:18},
 {name :'Bounty Hunter', DP:39, AP:4.0, Str:17, Agi:21, Int:16},
                                                                                                 ​18, Agi:22, Int:15},
 {name:'Guardian of Light', DP:38, AP:1.1, Str:16, Agi:15, Int:22},
 {name: 'Alchemist', DP:49, AP:0.6, Str:25, Agi:11, Int:25}
                                                                                                                     For heroes whose defense is greater than 40 and whose defense is less than 4, we can use Array’s filter method: 

Copy code

The code is as follows: var match = heroes.filter(function(e) { .

Compared with manually writing loop judgments, the filter method provides us with great convenience. But it is based on function callbacks, so you must write a function every time you use it, which is very cumbersome for simple queries, and the efficiency of using callbacks is also greatly reduced. But there is no way to do this. If you want to be simple, you must sacrifice a certain amount of performance. How perfect it would be if we could use simpler statements than this and fully enjoy the efficiency of code expansion. 


First imagine, if the above code can be written like this, and 
the query speed is the same as the handwritten traversal judgment
: 

Copy the code

The code is as follows:

var match = heroes.select('@DP>40 AND @AP<4'); It looks a bit like SQL, even the syntax has been changed? Wouldn't this mean that we would have to write a lot of script engine functions such as lexical analysis, semantic interpretation, etc. It would be impossible to handle even thousands of lines of code, and the efficiency would definitely be worse. . . If you think it's that complicated, then you haven't deeply understood the essence of the script. All scripting languages have interfaces for dynamically interpreting code at runtime, such as execute() of VBS; eval(), new Function() of JS, and even create a