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String with character repetition [closed]

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Can someone help me on this one? Given a string, I have to return a string in which each character (case-sensitive) is repeated once.
doubleChar("String") ==> "SSttrriinngg"
doubleChar("Hello World") ==> "HHeelllloo WWoorrlldd"
doubleChar("1234!_ ") ==> "11223344!!__ "
function doubleChar(str) {
}

You can use repeat() method for this like:
function doubleChar(str) {
return [...str].map(s => s.repeat(2)).join('')
}
console.log(doubleChar("String"))
console.log(doubleChar("Hello World"))
console.log(doubleChar("1234!_ "))

Try this:
const str = 'hello'
let arr = str.split('')
const double = arr.map(i => i += i).join('')
console.log(double)

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\"" }

Combine to get new variable name [closed]

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I need to get this: $('#anchor')
Where anc hor are variables themselves.
var firstPart = "anc"
var secondPart = "hor"
How do I do that? + to the question (sorry for that) if I have this structure:
<a id="233"></a><li>qwerty</li>
how do I addClass to this exact li that comes after #233?

First part:
$('#' + firstPart + secondPart); // $('#anchor')
Second part:
$('#123 + li').addClass('myclass');
http://www.w3.org/TR/CSS2/selector.html#adjacent-selectors

Answer1
var firstPart = "anc"
var secondPart = "hor"
var selector = "#" + firstPart + secondPart;
Then you can call it by $(selector) .
Answer 2:
$(function(){
$('#233 + li').addClass('ownclass');
});
Check http://jsfiddle.net/alaminopu/U2q6E/ for Answer 2.

'#anchor' is just a string. You use standard string concatination.
var str = '#' + firstPart + secondPart;
$(str)