[Steem-js] How to validate Username and Private Keys.

Hello, my friends.

Steem-js is official Javascript library for Steem.
you can read more about steem-js here

Today in Steemdevs Discord Server Someone asked a question:

Now I'm going to Answer This question.

Note: You can find another solution for this.

First we need to add steem-js to our js file.

in browser:

<script src="https://cdn.steemjs.com/lib/latest/steem.min.js"></script>

and in node.js:

first, you must install steem by npm: npm install steem --save
then, add this line to your js fildes.
var steem = require('steem');

We can get accounts info by:
var name = 'mahdiyari';
steem.api.getAccounts([name], function(err, result) { console.log(err,result); });

but we need only public posting key:
var name = 'mahdiyari';
steem.api.getAccounts([name], function(err, result) {
var pubWif = result[0].posting.key_auths[0][0];
});
pubWif will be Posting Public Key.

Asume private posting key is like below:
var privWif = 'mylongprivatepostingkey';

We can Check if privWif is valid for that pubWif or not.
steem.auth.wifIsValid(privWif, pubWif);

It will return true or false.
so we can use it like this:
var isvalid = steem.auth.wifIsValid(privWif, pubWif);
if(isvalid == true){
console.log(name+' Welcome.');
}else{
console.log('Wrong! Check your Private key.');
}

If user private posting key is valid, it will say mahdiyari Welcome.

Full Code:
var steem = require('steem');
var name = 'mahdiyari';
steem.api.getAccounts([name], function(err, result) {
var pubWif = result[0].posting.key_auths[0][0];
var privWif = 'mylongprivatepostingkey';
var isvalid = steem.auth.wifIsValid(privWif, pubWif);
if(isvalid == true){
console.log(name+' Welcome.');
}else{
console.log('Wrong! Check your Private key.');
}
});

this code is working fine for true Private Keys.
if you try with another character as privWif in above example, you will get an error.
we can remove this error by adding try{}catch(){}

Full code with try{}catch(){}:

var steem = require('steem');
var name = 'mahdiyari';
steem.api.getAccounts([name], function(err, result) {
var pubWif = result[0].posting.key_auths[0][0];
var privWif = 'mylongprivatepostingkey';
var isvalid;
try{ isvalid = steem.auth.wifIsValid(privWif, pubWif); }
catch(e){ isvalid = 'false'; }
if(isvalid == true){
console.log(name+' Welcome.');
}else{
console.log('Wrong! Check your Private key.');
}
});

If you have any question, ask in comments or join Steemdevs Discord Server.
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Regards,
2017-09-04