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+---
+title: JavaScript Comparison operation at a glance
+date: 2019-03-28 09:00:00
+tags:
+    - JavaScript
+category: tech
+keywords:
+    - Javascript
+    - ES2015
+    - ES6
+---
+
+When given a scenario like:
+
+```javascript
+console.log(null > -1) //true
+```
+
+It produces `true`, which makes me think `null` is treated as `0`. But when I run:
+```javascript
+console.log(null == 0) // false
+console.log(null > 0) // false
+console.log(null < 0) // false
+```
+They all output `false`!
+
+I googled a lot and finally found answers in [Ecma-262 Specification](http://www.ecma-international.org/ecma-262/8.0/#sec-abstract-equality-comparison).
+
+The comparison `x == y`, where x and y are values, produces true or false. Such a comparison is performed as follows:
+<!-- more -->
+```text
+1. If Type(x) is the same as Type(y), then return the result of performing Strict Equality Comparison x === y.
+2. If x is null and y is undefined, return true.
+3. If x is undefined and y is null, return true.
+4. If Type(x) is Number and Type(y) is String, return the result of the comparison x == ToNumber(y).
+5. If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x) == y.
+6. If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.
+7. If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
+8. If Type(x) is either String, Number, or Symbol and Type(y) is Object, return the result of the comparison x == ToPrimitive(y).
+9. If Type(x) is Object and Type(y) is either String, Number, or Symbol, return the result of the comparison ToPrimitive(x) == y.
+10. Return false.
+```
+
+Relational comparison is much more complex so I'm not copying that section. Read at the [spec website](http://www.ecma-international.org/ecma-262/8.0/#sec-abstract-relational-comparison).
+
+## TL;DR
+
+Anyway it seems that in `null == 0`, `null` is treated just as is, and **equality** comparison between `null` and `Number` always return **false** (No 10).
+But when it comes `null > -1`, `null` is conversed to 0 using [ToNumber()](http://www.ecma-international.org/ecma-262/8.0/#sec-tonumber) algorithm.
+
+Read more:
+* [https://github.com/getify/You-Dont-Know-JS/issues/1238](https://github.com/getify/You-Dont-Know-JS/issues/1238)
+* [http://www.ecma-international.org/ecma-262/8.0/#sec-abstract-relational-comparison](http://www.ecma-international.org/ecma-262/8.0/#sec-abstract-relational-comparison)
+* [http://www.ecma-international.org/ecma-262/8.0/#sec-tonumber](http://www.ecma-international.org/ecma-262/8.0/#sec-tonumber)