Sub string around a keyword in javascript

subStringAroundKeyword.js

/**
 * Returns a sub-string with the specified keyword in the middle.
 * @param text: Full statement with the keyword in it.
 * @param keyword: Keyword which you want to concentrate.
 * @param subStringLen: The length of the desired resultant string.
 * @param truncate: If true it will add '...' at the starting and ending of the resultant string.
 * @author sooryagangaraj
 * @return string
 */
function subStringAroundKeyword(text, keyword, subStringLen, truncate = true) {
    // Total chars in text
    const totalTextLen = text.length;
    // Number of chars needed around keyword
    var charsAroundNeeded = subStringLen - keyword.length

    // Starting and ending index for adjusting
    var startingIndex = text.toLowerCase().indexOf(keyword.toLowerCase())
    var endingIndex = startingIndex + keyword.length

    if (startingIndex === -1) return ""

    while (charsAroundNeeded > 0) {
        var indexChanged = false

        // Adjusting starting index
        if (startingIndex - 1 >= 0) {
            startingIndex -= 1
            charsAroundNeeded -= 1
            indexChanged = true
        }

        // Adjusting ending index
        if (endingIndex + 1 < totalTextLen && charsAroundNeeded > 0) {
            endingIndex += 1
            charsAroundNeeded -= 1
            indexChanged = true
        }

        // Reducing chars if there is nothing to get adjusted
        if (!indexChanged) {
            charsAroundNeeded -= 1
        }
    }

    // Checking if we can avoid three dots at the end if the keyword is within three positions from last
    let endingToTotalTextLen = totalTextLen - endingIndex;
    let isEndingToTotalTextLenWithin3 = endingToTotalTextLen > 0 && endingToTotalTextLen <= 3;
    if (isEndingToTotalTextLenWithin3) endingIndex = totalTextLen;

    // Checking if we can avoid three dots at the beginning if the keyword starts withing three positions from start
    let isStartingIndexWithing3 = startingIndex > 0 && startingIndex <= 3;
    if (isStartingIndexWithing3) startingIndex = 0;

    // Substring with keyword and around text.
    let resultingSubString = ((truncate && startingIndex > 0) ? "..." : "")
        + text.slice(startingIndex, endingIndex)
        + ((truncate && endingIndex < totalTextLen) ? "..." : "");

    return resultingSubString
}