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))

const string = "foo";
const substring = "oo";
console.log(string.includes(substring)); // true

<?php
if (str_contains('abc', '')) {
    echo "Checking the existence of the empty string will always return true";
}
?>

function mutation(arr) { let first = arr[0]; let second = arr[1]; return first.indexOf(second) !== -1;
}
console.log(mutation(["hello", "hel"]));

#is target in base?
def findSubstring(base, target): match = "" for x in range(0, len(base)): substring = base[0:len(base)-x] if substring == target: print("there is a match") match = substring if match == "": return "" else: return match
print(findSubstring("aaaaaaa", "aaa"))

# User input
main_string = input("Enter the main string: ")
substring = input("Enter the substring to search for: ")
# Check if substring is present in the main string
if substring in main_string: print("Substring found in the main string!")
else: print("Substring not found.")