RJK RJK - 2 years ago 88
Javascript Question

Javascript read external text file, pass text file data as parameter

Please check this fiddle: https://jsfiddle.net/dp0y4hrw/16/

This is JS to find longest compound word in an array of strings.

Instead of an array, I want this program to read a local txt file, consisting of over 100,000 lines of text. Then find longest compound words. Each line has one word.

I've tried using FileReader to get the data. I was able to correctly pass the data, but gave me trouble with some shared variables between 'addPrefix' and 'findPrefixes'.

I also tried using a promise, to account for the asynchronous behavior:

function readFile(event) {
var file = event.target.files[0];

if (file) {
new Promise(function(resolve, reject) {
var reader = new FileReader();
reader.onload = function (evt) {

reader.onerror = reject;

.catch(function(err) {

document.getElementById('file').addEventListener('change', readFile, false);

function findLongestWord(data) {

This still gives me an issue. What would be the best way to read the file so I can process the contents correctly in this situation?


// adds word as a prefix
var addPrefix = function (word) {
var i = 0;
var current = prefixes;
var char;

while (char = word[i++]) {
if (!current[char]) {
current[char] = {};
current = current[char];
current.word = true;
return current.word; //RETURNING CURRENT WORD HERE

// Finds the longest prefix we can make using the word.
var findPrefixes = function (word) {
var prefix = '';
var current = prefixes;
var found = [];
var i = 0;
var char;

while (char = word[i++]) {
if (!current[char]) {
// Move to the next character and add to the prefix.
current = current[char];
prefix += char;

return found;

//for each word in list, add to prefix
list.forEach(function (word) {
var prefix;

// If we can find a closest possible word, it may be possible to create a
// compound word - but we won't be able to check until we reach the end.
if ((prefix = findPrefixes(addPrefix())) && prefix.length) { //FINDPREFIXES USING ADDPREFIX HERE
prefixMatch.push([ word, prefix ]);


// Insert the word into the prefix tree.

EDIT 2: This is example of input text file:


Expected result is: longest: ratcatdogcat,catratdograt...2nd longest: catsdogcats,dogcatscats...number of compound words: 5

Answer Source

Use RegExp /\w+/g

\w Matches any alphanumeric character from the basic Latin alphabet, including the underscore.

x+ Matches the preceding item x 1 or more times

var list = data.match(/\w+/g);
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