ZX BASIC - Replace While, Repeat htm2tap, replace BEFORE submit JS

ZX Spectrum BASIC
REPEAT UNTIL:
325 REPEAT j
330   INPUT "ENTER NUMBER: ";N
335   IF N="10" THEN PRINT "Congrats":LET j=1
345 UNTIL j=1

REPEAT Translates to :
325 FOR j = 0 TO 1 STEP 0 : REM REPEAT
330   INPUT "ENTER NUMBER: ";N
335   IF N="10" THEN PRINT "Congrats":LET j=1
345 NEXT j : REM UNTIL
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WHILE UNTIL:
325 While j < 1
330   INPUT "ENTER NUMBER: ";N
335   IF N="10" THEN PRINT "Congrats":LET j=1
345 EndWhile

WHILE Translates to :
325 FOR i = NOT( j < 1 ) TO 0.5 STEP 0 : REM While
330 INPUT "ENTER NUMBER: ";N
335 IF N="10" THEN PRINT "Congrats":LET j=1
340 LET i = NOT ( j<1 )
345 NEXT i : REM ENDWhile



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Javascript replace BEFORE submit
https://stackoverflow.com/questions/4517366/change-form-values-after-submit-button-pressed

window.onload = function() {

  document.getElementById('theForm').onsubmit = function() {
    var txt = document.getElementById('txtSearch');
    txt.value = "updated " + txt.value;
  };
};