lots of modif:

script.js

@@ -4,6 +4,8 @@ const good_letter_color = "#3fbe00";
 const bad_letter_color = "#BE0000";
 const mid_letter_coloer = "#BF8200";
 var free_box = [1,1];
+let arrWords;
+readTextFile("words.txt");
 
 function change_color_good_letter(coord){
     var case_div = document.getElementById(coord);
@@ -50,9 +52,13 @@ function Supprimer() {
 }
 
 function Enter() {
+    if (free_box[1]==5 && free_box[0]!=6) {
+
+        verifLettres(word);
+        word="";
+    }
     free_box[0]+=1;
     free_box[1]=1;
-    verifLettres(word);
 }
 
 function verifLettres(aWord) {
@@ -87,4 +93,42 @@ function write_result(verif){
             change_color_bad_letter();
         }
     }
-}
+}
+
+function readTextFile(file) //Merci StackOverflow
+{
+    var rawFile = new XMLHttpRequest();
+    rawFile.open("GET", file, false);
+    rawFile.onreadystatechange = function ()
+    {
+        if(rawFile.readyState === 4)
+        {
+            if(rawFile.status === 200 || rawFile.status == 0)
+            {
+                var allText = rawFile.responseText;
+                arrWords=allText.split(/\r?\n/);
+            }
+        }
+    }
+    rawFile.send(null);
+
+}
+
+function verifWord() {
+
+    let exist = false;
+    if (word.length == 5)
+    {
+
+        for(let i = 0; i< arrWords.length;i++)
+        {
+             if(arrWords[i]==word)
+            {
+                exist = true;
+            }
+
+        }
+    }
+    return exist;
+
+}