Merge pull request #2296 from MetaMask/precision-fix

Fix precision to account for small wei increase.

2 files changed, 45 insertions, 4 deletions

diff --git a/test/unit/components/bn-as-decimal-input-test.js b/test/unit/components/bn-as-decimal-input-test.js
index 106b3a871..58ecc9c89 100644
--- a/test/unit/components/bn-as-decimal-input-test.js
+++ b/test/unit/components/bn-as-decimal-input-test.js
@@ -48,4 +48,42 @@ describe('BnInput', function () {
       checkValidity () { return true } },
     })
   })
+
+  it('can tolerate wei precision', function (done) {
+    const renderer = ReactTestUtils.createRenderer()
+
+    let valueStr = '1000000000'
+
+    const value = new BN(valueStr, 10)
+    const inputStr = '1.000000001'
+
+
+    let targetStr = '1000000001'
+
+    const target = new BN(targetStr, 10)
+
+    const precision = 9 // gwei precision
+    const scale = 9
+
+    const props = {
+      value,
+      scale,
+      precision,
+      onChange: (newBn) => {
+        assert.equal(newBn.toString(), target.toString(), 'should tolerate increase')
+        const reInput = BnInput.prototype.downsize(newBn.toString(), 9, 9)
+        assert.equal(reInput.toString(), inputStr, 'should tolerate increase')
+        done()
+      },
+    }
+
+    const inputComponent = h(BnInput, props)
+    const component = additions.renderIntoDocument(inputComponent)
+    renderer.render(inputComponent)
+    const input = additions.find(component, 'input.hex-input')[0]
+    ReactTestUtils.Simulate.change(input, { preventDefault () {}, target: {
+      value: inputStr,
+      checkValidity () { return true } },
+    })
+  })
 })
diff --git a/ui/app/components/bn-as-decimal-input.js b/ui/app/components/bn-as-decimal-input.js
index f3ace4720..d84834d06 100644
--- a/ui/app/components/bn-as-decimal-input.js
+++ b/ui/app/components/bn-as-decimal-input.js
@@ -31,7 +31,7 @@ BnAsDecimalInput.prototype.render = function () {
   const suffix = props.suffix
   const style = props.style
   const valueString = value.toString(10)
-  const newValue = this.downsize(valueString, scale, precision)
+  const newValue = this.downsize(valueString, scale)
 
   return (
     h('.flex-column', [
@@ -145,14 +145,17 @@ BnAsDecimalInput.prototype.constructWarning = function () {
 }
 
 
-BnAsDecimalInput.prototype.downsize = function (number, scale, precision) {
+BnAsDecimalInput.prototype.downsize = function (number, scale) {
   // if there is no scaling, simply return the number
   if (scale === 0) {
     return Number(number)
   } else {
     // if the scale is the same as the precision, account for this edge case.
-    var decimals = (scale === precision) ? -1 : scale - precision
-    return Number(number.slice(0, -scale) + '.' + number.slice(-scale, decimals))
+    var adjustedNumber = number
+    while (adjustedNumber.length < scale) {
+      adjustedNumber = '0' + adjustedNumber
+    }
+    return Number(adjustedNumber.slice(0, -scale) + '.' + adjustedNumber.slice(-scale))
   }
 }