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add gotcha re: lack of int #18

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29 changes: 24 additions & 5 deletions README.md
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Expand Up @@ -76,12 +76,12 @@ printDate(object.scheduledDate);
```
In this case if we expect that if ``` object.scheduledDate ``` is ``` undefined ``` then print current date or else print the scheduled date. But this *js-gotcha* will give unexpected result and you will loose half of your hair.

### 5. Load scripts in order of dependency requirements.
The simplified explanation of this issue is that a variable or function cannot be referenced or called prior to being defined elsewhere in the code. Where scripts require other scripts, or content requires a particular loading order, this may become more complex. In the following example, script1.js is loaded after the testVar1 function executes, thus varInScript1 is not defined and errors in the browser.
### 5. Load scripts in order of dependency requirements.
The simplified explanation of this issue is that a variable or function cannot be referenced or called prior to being defined elsewhere in the code. Where scripts require other scripts, or content requires a particular loading order, this may become more complex. In the following example, script1.js is loaded after the testVar1 function executes, thus varInScript1 is not defined and errors in the browser.

```
```
<html>
<head>
<head>
<script type="text/javascript">
function testVar1() {
if (varInScript1) {
Expand All @@ -97,4 +97,23 @@ The simplified explanation of this issue is that a variable or function cannot b
</html>
```

By extrapolating this use case into more complicated environments, implementing dependency handling solutions, such as RequireJS, may assist to track and handle dependency requirements.
By extrapolating this use case into more complicated environments, implementing dependency handling solutions, such as RequireJS, may assist to track and handle dependency requirements.

### X. There is only one type of number.
Numbers of the javascript Number type can be written with either as whole numbers or as decimals.
Unlike languages with distinct integer and float types, in javascript:
```js
0 === 0.0 // true
```
Numbers are stored in double-precision 64-bit binary format (a number between -2^53 -1 and 2^53 -1). Number also has three symbolic values: +Infinity (any number outside the largest possible number), -Infinity, and NaN.

The lack of an integer type makes javascript calculations slower and less precise.
For example, errors floating point arithmetic are common:
```js
let x = 0.2 + 0.1 // x will be 0.30000000000000004
```

This kind of error can be avoided by converting the numbers to a whole number during the calculation:
```js
let x = (0.2 * 10 + 0.1 * 10) / 10 // x will now be 0.3 as expected
```