Call a function after leaving input field

You can use onblur() or onfocusout(). It will call function once you click out of that text field.

Example:

function myFunction() {
    var x = document.getElementById("sometext");
    x.value = x.value.toUpperCase();
}

<input type="text" id="sometext" onfocusout="myFunction()">

Note: As from React 16, onFocusIn and onFocusOut have been replaced by onFocus and onBlur respectively. Hence you now have:

<input type='text' name='input_email' onBlur={this.validateEmail}/>

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