How can I correctly check if a string does NOT contain a specific word?

Question

I am currently trying to figure out how to solve the above named problem. Specifically I want to check if the string does not contain the word "stream" both in capital and lowercase letters.

Here's my code so far:

if (((gewaesser_name1.includes("Stream") == "false") ||
(gewaesser_name1.includes("stream") == "false")) &&
((gewaesser_name2.includes("Stream") == "false") ||
(gewaesser_name2.includes("stream") == "false")))
{var a= "..."}

The code does obviously not work as the results are not what I expect them to be. I also tried to use the indexOf method before using the following syntax variations:

gewaesser_name2.indexOf("stream") == -1
gewaesser_name2.indexOf("stream") < 0

None of these variations seem to work for me. Could anyone please give me a hint what's the problem here? I used the indexOf method before many times but always when I wanted to check if a string did contain a specific word, not the other way round.

Answer 1

I suggest to use String+toLowerCase and check with String#indexOf, because it works in every browser.

if (gewaesser_name1.toLowerCase().indexOf("stream") === -1 && gewaesser_name2.toLowerCase().indexOf("stream") === -1) {
    var a = "..."
}

Answer 2

indexOf() is the correct approach and the case issue can be easily resolved by forcing the test string to lower or upper case before the test using .toLowerCase() or .toUpperCase():

const lookupValue = "stream";
const testString1 = "I might contain the word StReAm and it might be capitalized any way.";
const testString2 = "I might contain the word steam and it might be capitalized any way.";

function testString(testData, lookup){
  return testData.toLowerCase().indexOf(lookup) === -1;
}

function prettyPrint(yesNo){
   return "The string does" + (yesNo ? " NOT" : "") + " contain \"stream\" in some form."
}

console.log(prettyPrint(testString(testString1, lookupValue)));
console.log(prettyPrint(testString(testString2, lookupValue)));