content fixes, #1646

1-js/02-first-steps/07-operators/3-primitive-conversions-questions/solution.md

@@ -0,0 +1,26 @@
+
+```js no-beautify
+"" + 1 + 0 = "10" // (1)
+"" - 1 + 0 = -1 // (2)
+true + false = 1
+6 / "3" = 2
+"2" * "3" = 6
+4 + 5 + "px" = "9px"
+"$" + 4 + 5 = "$45"
+"4" - 2 = 2
+"4px" - 2 = NaN
+7 / 0 = Infinity
+" -9  " + 5 = " -9  5" // (3)
+" -9  " - 5 = -14 // (4)
+null + 1 = 1 // (5)
+undefined + 1 = NaN // (6)
+" \t \n" - 2 = -2 // (7)
+```
+
+1. The addition with a string `"" + 1` converts `1` to a string: `"" + 1 = "1"`, and then we have `"1" + 0`, the same rule is applied.
+2. The subtraction `-` (like most math operations) only works with numbers, it converts an empty string `""` to `0`.
+3. The addition with a string appends the number `5` to the string.
+4. The subtraction always converts to numbers, so it makes `"  -9  "` a number `-9` (ignoring spaces around it).
+5. `null` becomes `0` after the numeric conversion.
+6. `undefined` becomes `NaN` after the numeric conversion.
+7. Space characters, are trimmed off string start and end when a string is converted to a number. Here the whole string consists of space characters, such as `\t`, `\n` and a "regular" space between them. So, similarly to an empty string, it becomes `0`.

1-js/02-first-steps/07-operators/3-primitive-conversions-questions/task.md

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+importance: 5
+
+---
+
+# Type conversions
+
+What are results of these expressions?
+
+```js no-beautify
+"" + 1 + 0
+"" - 1 + 0
+true + false
+6 / "3"
+"2" * "3"
+4 + 5 + "px"
+"$" + 4 + 5
+"4" - 2
+"4px" - 2
+7 / 0
+"  -9  " + 5
+"  -9  " - 5
+null + 1
+undefined + 1
+" \t \n" - 2
+```
+
+Think well, write down and then compare with the answer.