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Input text form field validation

I’m trying to customize my form.
There are 2 input text fields and milti-step form, so i want to validate certain input fields (if visitor taped some number or not), before move forward and before visitor clicks form button “Submit”

If there is a number - button “next step” will be displayed:

If input field is empty - button visibility will be “none”:

I found some custom code and paste my ID names:

('input').keyup(function(){ if(((’#node45’).val().length > 0) && (('#node46').val().length > 0)) ("#simple-button").css(“display”, “none”);
$("#simple-button").css(“display”, “block”);

but it doesn’t work…
Please, need help)))