在JavaScript / Nodejs中动态处理未定义变量的最佳实践

Question

Ok, maybe is not the best title, but I lacked inspiration, so here goes:

Let's say you have a "global" (not really) variable to store temporary data and sub data as random users interact with your server. Normally on the first interaction with your server, the main variable will be undefined so you need to handle that case.

Now, what puzzled me about this, is what's the best practice performance wise to do this if there are a lot of users and a lot way more interactions with the variable.

Puzzled? Yeah, I know, words are not my strong point so let me show you in code

So you have

var user_data = [];

Then a function that handles user interaction to store data

function writeData(uid, data_name, data)

Now, on first interaction, user_data[uid][data_name] is undefined, and so it's user_data[uid]

I know you can handle this 2 ways:

With if -

if(!user_data[uid]) user_data[uid] = {}
 user_data[uid][data_name] = data

With try/catch

try{user_data[uid][data_name] = data} 
catch(e) {user_data[uid] = {}; writeData(uid, data_name, data)}

The if will check on every interaction, and like I said there are a lot. Try catch will trigger once, but it has a cost as a block (afaik)

Which one is better? Or is there a another better way

Answer 1

@Nertan , There is a partiality in your proof :P . I have slightly tweeked the ternary way (same as the order of execution in if way). With this you can conclude.

 //var present = require('present'); function test(val,ud,fun) { var k = 10000000; var t = Date.now(); for(var i=0; i<k;i++) { var uid = Math.ceil(Math.random()*1000); fun(uid,ud,"value"); } var tf = Date.now()-t; return tf; } function setValue_Opp(uid,ud,value) { (!ud[uid] && (ud[uid] = {})) && (ud[uid].value = value); } function setValue_Try(uid,ud,value) { try{ ud[uid].value = value} catch(e){ ud[uid] = {}; setValue_Try(uid,ud,value)}; } function setValue_Cond(uid,ud,value) { if(!ud[uid]) ud[uid] = {} ud[uid].value = value; } var k1=0; var k2=0; var k3=0; for(var i=0;i<10;i++){ k1+=test(1,{}, setValue_Cond); k2+=test(2,{}, setValue_Try); k3+=test(3,{}, setValue_Opp); } console.log(k1,k2,k3) 

Answer 2

I feel we can take advantage of ES6 ternaries as below:

 let user_data = {} const writeData = (uid, data_name, data) => { ((user_data[uid] || (user_data[uid] = {})) && (user_data[uid][data_name] = data )) console.log(user_data) // perform write action } writeData('1',"test","test1"); writeData('2',"test","test2"); writeData('1',"test","test3"); 

Answer 3

Ok, so I had to rewrite the test because it doesn't work fine in the Snippet

So I made this for node.js:

 var present = require('present'); function test(val,ud,fun) { var k = 10000000; var t = present(); for(var i=0; i<k;i++) { var uid = Math.ceil(Math.random()*1000); fun(uid,ud,"value"); } var tf = present()-t; console.log("END "+val+" at "+tf); return tf; } function setValue_Opp(uid,ud,value) { (ud[uid] || (ud[uid] = {})) && (ud[uid].value = value); } function setValue_Try(uid,ud,value) { try{ ud[uid].value = value} catch(e){ ud[uid] = {}; setValue_Try(uid,ud,value)}; } function setValue_Cond(uid,ud,value) { if(!ud[uid]) ud[uid] = {} ud[uid].value = value; } var k1=0; var k2=0; var k3=0; for(var i=0;i<10;i++){ k1+=test(1,{}, setValue_Cond); k2+=test(2,{}, setValue_Try); k3+=test(3,{}, setValue_Opp); } console.log(k1,k2,k3) 

And in the end: 3244.328997004777 3695.0267750024796 3437.6855720058084

Which means:

The best is the classical if

The second best is condintional operators method

And the worst is the try-catch

So it seems the classics win

Edited:

With further tests thanks to @CRayen the best method is :

  (!ud[uid] && (ud[uid] = {})) && (ud[uid].value = value);