How to add a period after middle initial in full name build

Question

I am trying to build a full name from three fields (First, MI, and Last). If the middle initial field is blank, I do not want a period to appear in the assembled name. My code is below and when the MI field is blank, a period still appears between the first and last names. The partial_name is not being applied in this case.

    // Get field values 
var F_Name = this.getField('First_Name').value; 
var M_Name = this.getField('MI').value; 
var L_Name = this.getField('Last_Name').value; 

// Build full_name string
var full_name = F_Name + " " + M_Name +  ". " + L_Name;

// Build Partial Name string
var partial_name = F_Name + " " + L_Name;
 
if(M_Name="") {event.value = partial_name;
}
else {event.value = full_name;
}

screen capture of error

Answer 1

    // Get field values 
var F_Name = this.getField('First_Name').value; 
var M_Name = this.getField('MI').value; 
var L_Name = this.getField('Last_Name').value; 

// Build full_name string
var full_name = F_Name + " " + M_Name +  ". " + L_Name;

// Build Partial Name string
var partial_name = F_Name + " " + L_Name;
 
if(this.getField('MI').value=="") {
event.value = partial_name; 

// I think that's because you used single (=) instead of (==) or (===) and you //wrote If with a capital I 

}
else {event.value = full_name;
}