Develop Reference

Find the output using typeof function

I am writing a code. And here I have a problem how can I fix that. I have an input line, it takes a string or a number. So I need to check what is the output and get the answer. I need to give a simple solution. So I can't use functions or something like that.
let input = prompt('Enter your text.');
if (typeof input === "string") {
alert("You have string.");
} else if (typeof input === "number" && input > 30) {
alert("number more than 30");
} else if (typeof input === "number" && input < 30) {
alert("number less then 30");
}

prompt will always return a string.
If you want to check whether the string is composed purely of numerical values, you could use a regular expression:
if (/^[+-]?\d+(?:\.\d+)?$/.test(input)) {
// then it's purely numerical
const num = Number(input.trim());
// perform more operations on the number
} else {
// it's not composed of only numerical characters
}
If you don't want to use a regex, you can use Number alone, but then you'll also include values like Infinity which might not be desirable, and since Number('') gives 0, you'll have to check for that separately:
const num = Number(input);
if (input.trim().length && !Number.isNaN(num)) {
// then it's a number, use num
}
Another approach that I'd recommend is to avoid prompt entirely. Consider using a proper modal instead, such as a form with an input box and a submit button.
In such a case, if you want to require a numeric input, just do:
<input type="number">

I had a similar problem a few weeks ago and this is what I did:
function testNumber(test) {
if (isNaN(test) === false) {
console.log("this is a number");
} else {
console.log("this is not a number");
}
}
testNumber(4); // number
testNumber("4") // number
testNumber("string") // not a number
You can replace "test" for a variable if you don't want to use a function
if (isNaN(myVar) === false) {}
And you may want to add more checks if you want to differentiate between 4 and "4"

You can do
let input = prompt('Enter your text.');
if(isNaN(Number(input))){alert("You have string.")};
if (Number(input) > 30) {
alert("number more than 30");
} else if (Number(input) < 30) {
alert("number less then 30");
}
So it can change all Stringed-numbers to numbers and check if they are number with the isNaN function

Why this regular expression return false?

i have poor eng, Sorry for that.
i'll do my best for my situation.
i've tried to make SignUpForm using regular expression
The issue is that when i handle if statement using the regular expression
result is true at first, but after that, become false. i guess
below is my code(javascript)
$(document).ready(function () {
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/g; // more than 6 words
var pwCheck = /^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/; // more than 8 words including at least one number
var emCheck = /^([\w-]+(?:\.[\w-]+)*)#((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/; // valid email check
var signupConfirm = $('#signupConfirm'),
id = $('#id'),
pw = $('#pw'),
repw = $('#repw'),
email =$('#email');
signupConfirm.click(function () {
if(id.val() === '' || pw.val() === '' || email.val() === ''){
$('#signupForm').html('Fill the all blanks');
return false;
} else {
if (idCheck.test(id.val()) !== true) {
$('#signupForm').html('ID has to be more than 6 words');
id.focus();
return false;
} else if (pwCheck.test(pw.val()) !== true) {
$('#signupForm').html('The passwords has to be more than 8 words including at least one number');
pw.focus();
return false;
} else if (repw !== pw) {
$('#signupForm').html('The passwords are not the same.');
pw.empty();
repw.empty();
pw.focus();
return false;
}
if (emCheck.test(email.val()) !== true) {
$('#signupForm').html('Fill a valid email');
email.focus();
return false;
}
}
})
});
after id fill with 6 words in id input, focus has been moved to the password input because the condition is met.
but after i click register button again, focus move back ID input even though ID input fill with 6 words
i've already change regular expression several times. but still like this.
are there Any tips i can solve this issue?
I hope someone could help me.
Thank you. Have a great day

Do not use the global flag on your regexes. Your code should be:
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/;
When you match with the /g flag, your regex will save the state between calls, hence all subsequent matches will also include the previous inputs.

use
var idCheck = /^[a-z]+[a-z0-9]{5,19}$/
removing the g flag
and modify the line
else if (repw.val() !== pw.val()) {

How to determine if user is beginning new word in JS?

How would you, with JS or jQuery, determine if what the user is typing is a new word?
What I want to do:
I am writing a documentation tool with autocompletion for different types. If you type f.e. # it will populate Java Classes in a box, # would populate test classes, etc. Now I don't want to populate these values, if the user is writing something like an email like yourname#domain.com. So I need the values to populate only when it's the beginning of the word.
I am aware of keydown, keyup events, etc. I just don't know how to check for this certain kind of event properly.
One way would be to save every typed letter in a variable and then check if the previous "letter" was a space and if it was, we know it's a new word. Is this the best/most efficient way to do this?

One way is to check what's before the # in the input box, using selectionStart:
onload = function() {
var io = document.getElementById("io");
io.onkeypress = function(e) {
if(e.charCode == 64 && (
io.selectionStart == 0 || io.value[io.selectionStart-1].match(/\s/)))
document.getElementById("ac").innerHTML = "autocomplete!";
else
document.getElementById("ac").innerHTML = "";
}
}
<input id="io">
<div id="ac"></div>

Try this JSFiddle. I'm performing the check like so:
var text = $("#test").val();
if (text.length == 0 || text.charAt(text.length - 1).match(/[\s\b]/)) {
$("#result").html("new word");
} else {
$("#result").html("no new word");
}
You can easily adapt the .match() pattern if you like to include other characters as "whitespaces" (e.g. curly braces) for your Editor.

Assuming text is entered in a text input with id="txtchangedetection":
$("#txtchangedetection").change(function(){
console.log("The text has been changed.");
});
/*This is `JQuery`*/
I've understood you want to detect word changes in the input. Please precise if I'm wrong. What do you mean by 'new word' ?

One solution will be like this :
1- declare a variable "newWord = true"
2- with keydown event check if the key pressed is a space
if YES : newWord = true
if NO : newWord = false
var newWord=true;
$("#textarea").keydown(function(e){
if(e.keyCode == 32){
newWord=true;
}else{
newWord=false;
switch(e.keyCode){
//work to do
}
}
})

use keypress on your input field... populate the array inside the if with your special chars
if(prev == 13 || prev == 32 || $('#doc').val().length==0 || prev==null){
listen = true;
}else{
listen = false;
}
prev = e.which;
if(listen && $.inArray(String.fromCharCode(e.which),["#","#"]) != -1){
e.preventDefault();
alert("populate box here");
listen = false;
prev = null;
}
the fiddle https://jsfiddle.net/6okfqub4/

The if statement not working properly in Javascript

I am trying to create a logic that if anyone enters "<p>" and "</p>" characters inside <textarea>, then only Jquery should show the win message.I have a textarea with class html, a h2 with class result which shows win or loss.By now, I have this code:
var html = $('.html').val();
if(html.indexOf("</p>" && "<p>") === -1)
{
document.getElementById("result").innerHTML = "You lost it.";
}
else{
document.getElementById("result").innerHTML = "Hurray!You won";
}
But, this code is only checking if the <p> is there and not checking for </p>.So what can I do....

The expression "</p>" && "<p>" is equivalent to "<p>" -- && evaluates each of its arguments from left to right, and returns the last truthy argument. Since both strings are truthy, what you wrote is effectively:
if (html.indexOf("<p>") === -1)
If you want to test whether a string contains two substrings, you have to call indexOf separately for each of them:
if (html.index("</p>") !== -1 && html.indexOf("<p>") !== -1)

From MDN (Logical Operators) - Logical And (&&):
Returns expr1 if it can be converted to false; otherwise, returns
expr2. Thus, when used with Boolean values, && returns true if both
operands are true; otherwise, returns false.
</p> isn't being evaluated as false, so the second value is returned which is <p>.
This means that you're only checking for the index of <p>. Try this instead:
var html = $('.html').val();
if (html.indexOf("</p>") === -1 && html.indexOf("<p>") === -1) {
document.getElementById("result").innerHTML = "You lost it.";
}
else {
document.getElementById("result").innerHTML = "Hurray! You won";
}

.indexOf takes a single string as an argument. You cannot combine string elements together using && like that.
The simplest way to modify your code would be to make two separate checks, one for the opening tag and one for the close:
if (html.indexOf("</p>") !== -1 && html.indexOf("<p>") !== -1)
This makes two separate checks for the two strings.
Alternatively, you could create a jQuery object from the HTML fragment inside your <textarea>, then check that it has no children that are <p> tags:
if ($('<div>'+html+'</div>').find('p').length > 0) {
// the textarea contains some <p> tags
}

Javascript Replace - Regular Expression

I need to replace a code example: OD3 - The first must always be alpha character, 2nd alphanumeric and the last must always be numeric. What's the regular expression to check and replace the first and regulate the rest to enter correctly? A user could enter in the number 0 instead of the letter O, so I want to correct it immediately...
this is what I have so far: onkeyup="this.value=this.value.replace(/[^a-zA-z]/g,'')

First, I'd suggest just indicating the error to a user instead of replacing the values. Something like
oninput="if (! /^[a-z][a-z0-9]\d$/i.test(this.value) ) displayMessage('incorrect code');"
If you definitely have to replace the value on the fly, you could do somthing like that:
oninput='validateValue()';
...
function validateValue() {
var val = this.value;
if (! /[a-z]/i.test(val[0]) this.value = '';
else if (! /[a-z0-9]/i.test(val[1]) this.value = val.slice(0,1);
else if (! /\d/.test(val[2]) this.value = val.slice(0,2);
}

Better have like this.
onkeyup="testRegex(this.value)";
It is not .replace() it is .test()
function testRegex(value) {
if(value.test(/[^a-zA-z]/g)) {
alert("Please enter correct value");
return false;
}
}