Can someone please explain this strange behavior in Javascript? When I do comparisons using the match() method I don't get the expected result.
var mat_1 = "wpawn";
var mat_2 = "wRook";
//compare both; do they have the same first letter?
alert(mat_1.match(/^\w/) + " seems equal to " + mat_2.match(/^\w/));
if (mat_1.match(/^\w/) === mat_2.match(/^\w/)) {
alert("They are really equal")
}
//another approach
if (mat_1[0] === mat_2[0]) {
alert("Yes! Equals")
}
match produces an array. You should really use an array comparison function, but for the sake of simple demonstration, try this - the first match value is selected and compared. All 3 alerts are triggered:
var mat_1 = "wpawn";
var mat_2 = "wRook";
//compare both; do they have the same first letter?
alert(mat_1.match(/^\w/)+" seems equal to "+mat_2.match(/^\w/));
if(mat_1.match(/^\w/)[0] === mat_2.match(/^\w/)[0]){alert("They are really equal")}
//another approach
if(mat_1[0] === mat_2[0]){alert("Yes! Equals")}
Match returns an array of matches:
String.prototype.match(pattern: Regex): Array<string>
Your first evaluation will always fail as you are comparing two arrays.
This is the correct way for what you are trying to achieve.
'myWord'.match(/^\w/)[0] == 'mIsTeRy'.match(/^\w/)[0]
Although if you wanna truly use the regex to check the first letter, I wouldn't recommend it. Too much overhead for something too trivial (just my two cents).
Have fun coding! :)
in the following lines of code you are checking the variables mat_1 and mat_2 for whether both the words starts with 'w', btw match() returns an array
if (mat_1.match(/^\w/) === mat_2.match(/^\w/)) {
alert("They are really equal")
}
you can try something like
if (["w"] === ["w"]) {
console.log("seems equal");
} else {
console.log("not equal");
}
for array comparison you can check this post
what you have to do here is
if (["w"][0] === ["w"][0]) { // match for the elements in the array
console.log("seems equal");
} else {
console.log("not equal");
}
Related
I trying to convert number to boolean,
but my if condition always run the else block statements.
if ( !($(document).find($('.formSectionWrapper').length)) ) {
console.log('IF')
} else {
console.log('ElSE')
}
when length is 0 it runs else and when it is greater than 0 it run else block again!
What is my mistake?
Just change
if(!($(document).find($('.formSectionWrapper').length)))
to
if(!($(document).find($('.formSectionWrapper')).length))
Note the parenthesis.
In Javascript 0 is falsy and positive numbers are truithy
so you can just check on the number.
To answer your question:
Your logic looks wrong because of your ! you are inverting the logic which is likely confusing you.
According to jQuery Doc find, you find an element not the length.
Description: Get the descendants of each element in the current set of
matched elements, filtered by a selector, jQuery object, or element.
Then you apply the if...else statement on the length.
So here is how your code shall look like
const formSectionWrapper = $('.formSectionWrapper');
//const formSectionWrapper = $(document).find('.formSectionWrapper');
if ( !formSectionWrapper.length ) {
console.log('IF')
} else {
console.log('ElSE')
}
Hello I'm trying to understand recursion in JavaScript.
So far I have:
function countVowels(string) {
let vowelCount = 0;
// if we're not at the end of the string,
// and if the character in the string is a vowel
if (string.length - 1 >= 0 && charAt(string.length -1) === "aeiouAEIOU") {
//increase vowel count every time we iterate
countVowels(vowelCount++);
}
return vowelCount;
}
First of all, this is giving me issues because charAt is not defined. How else can I say "the character at the current index" while iterating?
I can't use a for-loop - I have to use recursion.
Second of all, am I using recursion correctly here?
countVowels(vowelCount++);
I'm trying to increase the vowel count every time the function is called.
Thanks for your guidance.
If you're interested, here is a version that does not keep track of the index or count, which might illuminate more about how the recursion can be done.
function countVowels(string) {
if (!string.length) return 0;
return (
"aeiou".includes(string.charAt(0).toLowerCase()) +
countVowels(string.substr(1))
);
}
console.log(countVowels("")); // 0
console.log(countVowels("abcde")); // 2
console.log(countVowels("eee")); // 3
// Note that:
console.log('"hello".substr(1)', "hello".substr(1)) // ello
console.log('"hello".charAt(0)', "hello".charAt(0)) // h
console.log('"aeiou".includes("a")', "aeiou".includes("a")) // true
console.log('"a".includes("aeiou")', "a".includes("aeiou")) // false
Our base case is that the string is empty, so we return 0.
Otherwise, we check if the first character in the string is a vowel (true == 1 and false == 0 in javascript) and sum that with counting the next (smaller by one) string.
You are making two mistakes:
You should have three parameters string , count(count of vowels) and current index i.
You should use includes() instead of comparing character with "aeiouAEIOU"
function countVowels(string,count= 0,i=0) {
if(!string[i]) return count
if("aeiou".includes(string[i].toLowerCase())) count++;
return countVowels(string,count,i+1);
}
console.log(countVowels("abcde")) //2
As asked by OP in comments "Can you please explain why it'sif("aeiou".includes(string[i].toLowerCase())) instead of if(string[i].includes("aeiou".toLowerCase()))"
So first we should know what includes does. includes() checks for string if it includes a certain substring passed to it or not. The string on which the method will be used it will be larger string and the value passed to includes() be smaller one.
Wrong one.
"a".includes('aeiou') //checking if 'aeiou' is present in string "a" //false
Correct one.
"aeiou".includes('a') //checking if 'a' is present in string "aeiou" //true
One possible solution would be:
function countVowels(string, number) {
if (!string) return number;
return countVowels(string.slice(1), 'aeiouAEIOU'.includes(string[0])? number + 1 : number);
}
// tests
console.log('abc --> ' + countVowels('abc', 0));
console.log('noor --> ' + countVowels('noor', 0));
console.log('hi --> ' + countVowels('hi', 0));
console.log('xyz --> ' + countVowels('xyz', 0));
and you should call your function like: countVowels('abc', 0)
Notes about your solution:
you always reset vowelCount inside your function, this usually does not work with recursion.
you defined your function to accept a string, but recall it with an integer in countVowels(vowelCount++); this it will misbehave.
always remember that you have to define your base case first thing in your recursion function, to make sure that you will stop sometime and not generate an infinite loop.
Alternative ES6 solution using regex and slice() method. Regex test() method will return true for vowels and as stated in a previous answer JavaScript considers true + true === 2.
const countVowels = str => {
return !str.length ? 0 : /[aeiou]/i.test(str[0]) + countVowels(str.slice(1));
}
I have a function to test if a prompt input is a number, like so:
function myFunction()
{
var person = prompt("Please enter your name", "");
if (person != null)
{
if(isNaN(person))
{
document.write("hello " + person + "<br><br>");
}
else
document.write("You gave me a number");
}
else
{
document.write("You didn't answer.<br><br>");
}
}
but every time I enter a number it keeps outputting hello + the number. I've been googling this function for quite some time and it doesn't make sense to me, it seems like it should work. Why is person returning true?
NaN is a special value in Javascript. What isNaN does is check to see if the value passed is equal* to this special value. If you want to check if something is, say, not a stream of numbers, you can use a regular expression:
if (!/^\d+(\.\d+)?/.exec(person)) {
Or parse the value as a number and see if it converts back to the same string:
var n = parseFloat(person);
if (n.toString() !== person) {
*There's a reason that we don't use === but it's outside the scope of this answer.
The isNaN function checks if a value is NaN. NaN is a value that occurs when making operations that require numbers with non-numbers. Please see the documentation.
However the function does not check if the value is of type number. Too check if a value is of type number use the typeof operator
typeof person === 'number'
Your code is the correct way of using the isNaN method. However for anyone else reading this post I have seen a strange anomaly where the documented usage of IsNaN hasn't worked properly and I got around the problem by combining the parseInt method with the IsNaN method. According to the W3c web site (https://www.w3schools.com/jsref/jsref_isnan.asp) the IsNan('123') should return false and IsNan('g12') should return true, but I've seen scenarios where this isn't the case.
If you're having trouble getting the documented methods to work try this code below:
var unitsToAdd = parseInt($('#unitsToAdd').val());
if(isNaN(unitsToAdd)) {
alert('not a number');
$('#unitsToAdd').val('1');
returnVal = false;
}
Alternatively you can try this method which is well tested.
function isNumber(searchValue) {
var found = searchValue.search(/^(\d*\.?\d*)$/);
//Change to ^(\d*\.?\d+)$ if you don't want the number to end with a . such as 2.
//Currently validates .2, 0.2, 2.0 and 2.
if(found > -1) {
return true;
}
else {
return false;
}
}
Hope this helps.
I have topdatedata value as 222
I have these 3 conditions specified
if((topDateData<250)&&(topDateData>25))
{
alert('one');
}
else if((topDateData>300)&&(topDateData<300))
{
alert('Two');
}
else
{
alert('Three');
}
My questions is why is it getting the value as alert(3) and not alert(one)??
When explicitly setting the value to 222, I see 'one' get alerted: http://jsfiddle.net/Wvjfa/
You should debug your actual value ( alert(topDateData); if you like) and see if it really is what you think it is.
Beyond that, Matt Ball is right, your second condition is borked. Also lonesomeday and Kerry are right about your variable case not matching between your question and the posted code.
Javascript is case sensitive, is topdatedata = 222 or topDateData = 222?
it's much safer just to set one value - as you're second criteria looks dodgy
var topDateData = 222;
if(topDateData > 300)
{
alert('two');
}
else if(topDateData > 250)
{
alert('');
}
else if(topDateData > 25)
{
alert('One');
}
else
{
alert('Three');
}
start with the one that's hardest to satisfy (in this example the highest) and then work your way down. It's much easier to follow. Other than that it should work, as per the other comments on here
My guess is that you have a string.
var trueBool = '222' < '250'; //true
var falseBool = '222' > '25'; //false
To debug if topDateData is a String or not, do the following:
alert(topDateData + 1);//outputs '2221' if a string, and '223' if a number
Here's a fiddle showing the difference.
UPDATE:
I've tested alert(('222' < 250) && ('222' > 25)); and that outputs true. However, I'm not sure all JavaScript compilers will be smart enough to convert the string to a number first. You should run the same test and see if true is the output on your browser.
It looks like your topDateData variable contains a string value "222" instead of an integer.
You could try to cast to an integer this way:
topDateData = parseInt(topDateData);
...
This question already has answers here:
How to check whether a string contains a substring in JavaScript?
(3 answers)
Closed 5 years ago.
I have a shopping cart that displays product options in a dropdown menu and if they select "yes", I want to make some other fields on the page visible.
The problem is that the shopping cart also includes the price modifier in the text, which can be different for each product. The following code works:
$(document).ready(function() {
$('select[id="Engraving"]').change(function() {
var str = $('select[id="Engraving"] option:selected').text();
if (str == "Yes (+ $6.95)") {
$('.engraving').show();
} else {
$('.engraving').hide();
}
});
});
However I would rather use something like this, which doesn't work:
$(document).ready(function() {
$('select[id="Engraving"]').change(function() {
var str = $('select[id="Engraving"] option:selected').text();
if (str *= "Yes") {
$('.engraving').show();
} else {
$('.engraving').hide();
}
});
});
I only want to perform the action if the selected option contains the word "Yes", and would ignore the price modifier.
Like this:
if (str.indexOf("Yes") >= 0)
...or you can use the tilde operator:
if (~str.indexOf("Yes"))
This works because indexOf() returns -1 if the string wasn't found at all.
Note that this is case-sensitive.
If you want a case-insensitive search, you can write
if (str.toLowerCase().indexOf("yes") >= 0)
Or:
if (/yes/i.test(str))
The latter is a regular expression or regex.
Regex breakdown:
/ indicates this is a regex
yes means that the regex will find those exact characters in that exact order
/ ends the regex
i sets the regex as case-insensitive
.test(str) determines if the regular expression matches str
To sum it up, it means it will see if it can find the letters y, e, and s in that exact order, case-insensitively, in the variable str
You could use search or match for this.
str.search( 'Yes' )
will return the position of the match, or -1 if it isn't found.
It's pretty late to write this answer, but I thought of including it anyhow. String.prototype now has a method includes which can check for substring. This method is case sensitive.
var str = 'It was a good date';
console.log(str.includes('good')); // shows true
console.log(str.includes('Good')); // shows false
To check for a substring, the following approach can be taken:
if (mainString.toLowerCase().includes(substringToCheck.toLowerCase())) {
// mainString contains substringToCheck
}
Check out the documentation to know more.
Another way:
var testStr = "This is a test";
if(testStr.contains("test")){
alert("String Found");
}
** Tested on Firefox, Safari 6 and Chrome 36 **
ECMAScript 6 introduces String.prototype.includes, previously named contains.
It can be used like this:
'foobar'.includes('foo'); // true
'foobar'.includes('baz'); // false
It also accepts an optional second argument which specifies the position at which to begin searching:
'foobar'.includes('foo', 1); // false
'foobar'.includes('bar', 1); // true
It can be polyfilled to make it work on old browsers.
The includes() method determines whether one string may be found within another string, returning true or false as appropriate.
Syntax :-string.includes(searchString[, position])
searchString:-A string to be searched for within this string.
position:-Optional. The position in this string at which to begin searching for searchString; defaults to 0.
string = 'LOL';
console.log(string.includes('lol')); // returns false
console.log(string.includes('LOL')); // returns true
You can use this Polyfill in ie and chrome
if (!('contains' in String.prototype)) {
String.prototype.contains = function (str, startIndex) {
"use strict";
return -1 !== String.prototype.indexOf.call(this, str, startIndex);
};
}
If you are capable of using libraries, you may find that Lo-Dash JS library is quite useful. In this case, go ahead and check _.contains() (replaced by _.includes() as of v4).
(Note Lo-Dash convention is naming the library object _.
Don't forget to check installation in the same page to set it up for your project.)
_.contains("foo", "oo"); // → true
_.contains("foo", "bar"); // → false
// Equivalent with:
_("foo").contains("oo"); // → true
_("foo").contains("bar"); // → false
In your case, go ahead and use:
_.contains(str, "Yes");
// or:
_(str).contains("Yes");
..whichever one you like better.
I know that best way is str.indexOf(s) !== -1; http://hayageek.com/javascript-string-contains/
I suggest another way(str.replace(s1, "") !== str):
var str = "Hello World!", s1 = "ello", s2 = "elloo";
alert(str.replace(s1, "") !== str);
alert(str.replace(s2, "") !== str);
You can also check if the exact word is contained in a string. E.g.:
function containsWord(haystack, needle) {
return (" " + haystack + " ").indexOf(" " + needle + " ") !== -1;
}
Usage:
containsWord("red green blue", "red"); // true
containsWord("red green blue", "green"); // true
containsWord("red green blue", "blue"); // true
containsWord("red green blue", "yellow"); // false
This is how jQuery does its hasClass method.
you can define an extension method and use it later.
String.prototype.contains = function(it)
{
return this.indexOf(it) != -1;
};
so that you can use in your page anywhere like:
var str="hello how are you";
str.contains("are");
which returns true.
Refer below post for more extension helper methods.
Javascript helper methods
None of the above worked for me as there were blank spaces but this is what I did
tr = table.getElementsByTagName("tr");
for (i = 0; i < tr.length; i++) {
td = tr[i].getElementsByTagName("td")[0];
bottab.style.display="none";
bottab2.style.display="none";
if (td) {
var getvar=td.outerText.replace(/\s+/, "") ;
if (getvar==filter){
tr[i].style.display = "";
}else{
tr[i].style.display = "none";
}
}
}