1 files changed, 46 insertions, 18 deletions

diff --git a/packages/instant/src/components/scaling_amount_input.tsx b/packages/instant/src/components/scaling_amount_input.tsx
index cfbf3b7cc..5dc719293 100644
--- a/packages/instant/src/components/scaling_amount_input.tsx
+++ b/packages/instant/src/components/scaling_amount_input.tsx
@@ -1,8 +1,11 @@
+import { BigNumber } from '@0x/utils';
 import * as _ from 'lodash';
 import * as React from 'react';
 
+import { Maybe } from '../types';
+
 import { ColorOption } from '../style/theme';
-import { BigNumberInput } from '../util/big_number_input';
+import { maybeBigNumberUtil } from '../util/maybe_big_number';
 import { util } from '../util/util';
 
 import { ScalingInput } from './scaling_input';
@@ -12,19 +15,44 @@ export interface ScalingAmountInputProps {
     maxFontSizePx: number;
     textLengthThreshold: number;
     fontColor?: ColorOption;
-    value?: BigNumberInput;
-    onChange: (value?: BigNumberInput) => void;
+    value?: BigNumber;
+    onAmountChange: (value?: BigNumber) => void;
     onFontSizeChange: (fontSizePx: number) => void;
 }
+interface ScalingAmountInputState {
+    stringValue: string;
+}
 
-export class ScalingAmountInput extends React.Component<ScalingAmountInputProps> {
+const { stringToMaybeBigNumber, areMaybeBigNumbersEqual } = maybeBigNumberUtil;
+export class ScalingAmountInput extends React.Component<ScalingAmountInputProps, ScalingAmountInputState> {
     public static defaultProps = {
-        onChange: util.boundNoop,
+        onAmountChange: util.boundNoop,
         onFontSizeChange: util.boundNoop,
         isDisabled: false,
     };
+    public constructor(props: ScalingAmountInputProps) {
+        super(props);
+        this.state = {
+            stringValue: _.isUndefined(props.value) ? '' : props.value.toString(),
+        };
+    }
+    public componentDidUpdate(): void {
+        const parsedStateValue = stringToMaybeBigNumber(this.state.stringValue);
+        const currentValue = this.props.value;
+
+        if (!areMaybeBigNumbersEqual(parsedStateValue, currentValue)) {
+            // we somehow got into the state in which the value passed in and the string value
+            // in state have differed, reset state
+            // we dont expect to ever get into this state, but let's make sure
+            // we reset if we do since we're dealing with important numbers
+            this.setState({
+                stringValue: _.isUndefined(currentValue) ? '' : currentValue.toString(),
+            });
+        }
+    }
+
     public render(): React.ReactNode {
-        const { textLengthThreshold, fontColor, maxFontSizePx, value, onFontSizeChange } = this.props;
+        const { textLengthThreshold, fontColor, maxFontSizePx, onFontSizeChange } = this.props;
         return (
             <ScalingInput
                 maxFontSizePx={maxFontSizePx}
@@ -32,7 +60,7 @@ export class ScalingAmountInput extends React.Component<ScalingAmountInputProps>
                 onFontSizeChange={onFontSizeChange}
                 fontColor={fontColor}
                 onChange={this._handleChange}
-                value={!_.isUndefined(value) ? value.toDisplayString() : ''}
+                value={this.state.stringValue}
                 placeholder="0.00"
                 emptyInputWidthCh={3.5}
                 isDisabled={this.props.isDisabled}
@@ -40,16 +68,16 @@ export class ScalingAmountInput extends React.Component<ScalingAmountInputProps>
         );
     }
     private readonly _handleChange = (event: React.ChangeEvent<HTMLInputElement>): void => {
-        const value = event.target.value;
-        let bigNumberValue;
-        if (!_.isEmpty(value)) {
-            try {
-                bigNumberValue = new BigNumberInput(value);
-            } catch {
-                // We don't want to allow values that can't be a BigNumber, so don't even call onChange.
-                return;
-            }
-        }
-        this.props.onChange(bigNumberValue);
+        const sanitizedValue = event.target.value.replace(/[^0-9.]/g, ''); // only allow numbers and "."
+        this.setState({
+            stringValue: sanitizedValue,
+        });
+
+        // Trigger onAmountChange with a valid BigNumber, or undefined if the sanitizedValue is invalid or empty
+        const bigNumberValue: Maybe<BigNumber> = _.isEmpty(sanitizedValue)
+            ? undefined
+            : stringToMaybeBigNumber(sanitizedValue);
+
+        this.props.onAmountChange(bigNumberValue);
     };
 }