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Need help to understand Vue.js function [closed]

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I have an assignment to make calculator using vue.js.
Much of it works, I'm confused about how to implement the '=' function.
I found this piece of code in an article that does something similar but I don't understand what it does. Can someone explain it?
https://scotch.io/tutorials/build-a-scientific-calculator-with-vuejs
I found this Piece of code:
if ((app.current).indexOf("^") > -1) {
var base = (app.current).slice(0, (app.current).indexOf("^"));
var exponent = (app.current).slice((app.current).indexOf("^") + 1);
app.current = eval("Math.pow(" + base + "," + exponent + ")");
} else {
app.current =app.current
}
Can someone please explain what the above function does, line-by-line?

// checks if app.current have '^' by getting the index
// if the method indexOf doesn't find anything it return -1
if (app.current.indexOf('^') > -1) {
// gets the first element till the index where it found '^'
var base = app.current.slice(0, app.current.indexOf('^'));
// gets the number after the 'ˆ'
var exponent = app.current.slice(app.current.indexOf('^') + 1);
// eval is evil
// it gets the string and transfoms into valid code
// wich means to do the operation
app.current = eval('Math.pow(' + base + ',' + exponent + ')');
} else {
// if it doesn't find the index it keeps the same value
app.current = app.current;
}
https://javascriptweblog.wordpress.com/2010/04/19/how-evil-is-eval/

find all substrings between ${ and } in javascript [closed]

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i have collections of text with some text between ${ and } like "this is ${test} string ${like}". How can I extract all there strings. Output : test,like

try
match(/{[\w\d]+}/g);
example
"{asdas}32323{234}".match(/{[\w\d]+}/g); //outputs ["{asdas}", "{234}"]
It will return with { and } with the matches which you can remove from the resultset by
"{asdas}32323{234}".match(/{[\w\d]+}/g).map(function(value){return value.substring(1, value.length-1)}); //outputs ["asdas", "234"]

you can try:
"this is ${test} string ${like}".match(/\${\w*}/g).map(function(str){return str.slice(2,-1)})
//["test", "like"]

Try this
var str = "this is ${test} string ${like}";
var txt = str.match(/{[\w\d]+}/g);
for(var i=0; i < txt.length; i++) {
txt[i] = txt[i].replace(/[{}]/g, '');
alert(txt[i]);
}

Syntax error js object to json [closed]

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Hello i'm using Backbone here i have an issue, my 'history' attribute will be
history = history + ' * ' + 'Attribute "used" modified from ' + !this.changed.used + ' to ' + this.changed.used + ' by ' + LOGGED_USER.get("fisrtName") + " " + LOGGED_USER.get("name") + ' the ' + (new Date());
But when i do
this.set("history", history);
var json = JSON.stringify(this.toJSON())
the json returned is kind of corrupted with \
Any idea ?

Because the " needs to be escaped in strings, it is not corrupted.
{ "key" : "I am \"valid\"" }

How to execute if condition based on a value from query string in javascript/jquery? [closed]

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I've a variable called url as follows :
url = "http://56.177.59.250/static/ajax.php?core[ajax]=true&core[call]=prj_name.contactform&width=400&core[security_token]=c7854c13380a26ff009a5cd9e6699840"
Now I want to use if condition only if core[call] is equal to the value it currently has i.e. prj_name.contactform otherwise not.
How should I do this since the parameter from query-string is in array format?

Just use String.indexOf and check if it is present (that is not -1, which means it doesn't exist)
if(url.indexOf("core[call]=prj_name.contactform") > -1){
// valid. Brew some code here
}

You can use location.search :
<script>
function get(name) {
name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
results = regex.exec(location.search);
return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}
if(get("core[call]") == "prj_name.contactform"){
alert('ok');
}else{
alert('no');
}
</script>

Some <div>s with a for loop [closed]

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I have a for loop and I want to create many <div>s with it.
I want to give the <div>s am ID from a varible.
Here's the code:
var text = $("#cont").text();
count = 1;
for (var i = 1; i <= 10; i++) {
text += "<div class='ball' id='ball'" + count + "></div><br />";
count++;
}

You've messed up your quotes:
text += "<div class='ball' id='ball" + count + "'></div><br />";
Your code had the single quote wrong and produced this:
<div class='ball' id='ball'5>
The number needs to be inside.

I'm a bit confused what your question is: It looks like you've already got the logic to do what you've specified.
That said, I see a probable error that may be confusing you: You're closing the single-quote on id='ball' before you concatenate the count variable. That will result in the div element not having that number as part of its id. Here's a corrected version of the code:
var text = $("#cont").text();
count = 1;
for (var i = 1; i <= 10; i++) {
text += "<div class='ball' id='ball" + count + "'></div><br />";
count++;
}