const cleanNumber = number.replace(/[^0-9]/g, "");

​

this.setState({

  cleanNumber

});

<TextInput 

   style={styles.textInput}

   keyboardType='numeric'

   onChangeText={(text)=> this.onChanged(text)}

   value={this.state.myNumber}

   maxLength={10}  //setting limit of input

/>

​

keyboardType='numeric'

const onChanged = (text) => {

        let newText = '';

        let numbers = '0123456789';

        for (var i=0; i < text.length; i++) {

            if(numbers.indexOf(text[i]) > -1 ) {

                newText = newText + text[i];

            }

            else {

                alert("please enter numbers only");

            }

        }

        setNumber(newText);

    }