Docs: document E057, E058, E059

Author: strager

docs/errors/E057.md

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+# E057: use of undeclared variable
+
+```config-for-examples
+{
+  "globals": {
+    "isHappy": true
+  }
+}
+```
+
+It is an error to use a function or variable without declaring it:
+
+    consol.write("Hello, world!");
+    const one = Math.sin(pi/2);
+
+    function encrypt() {
+      return data ^ 0x13371337;
+    }
+
+    if (isHappy) {
+      let emotion = "happy";
+    } else {
+      let emotion = "sad";
+    }
+    console.log("I am " + emotion);
+
+    function MyComponent({}) {
+      let [pressed, setPressed] = useState(false);
+    }
+
+    google.charts.load('current', {'packages':['corechart']});
+
+To fix this error, fix the name of the function or variable:
+
+    console.write("Hello, world!");
+    const one = Math.sin(Math.pi/2);
+
+Alternatively, declare the function or variable:
+
+    function encrypt(data) {
+      return data ^ 0x13371337;
+    }
+
+Alternatively, move the declaration of the variable into an outer scope:
+
+    let emotion;
+    if (isHappy) {
+      emotion = "happy";
+    } else {
+      emotion = "sad";
+    }
+    console.log("I am " + emotion);
+
+Alternatively, import the function or variable:
+
+    import { useState } from "react";
+    function MyComponent({}) {
+      let [pressed, setPressed] = useState(false);
+    }
+
+Alternatively, if the function or variable is global in your environment, [write
+a quick-lint-js.config file](https://quick-lint-js.com/config/).

docs/errors/E058.md

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+# E058: variable used before declaration
+
+```config-for-examples
+{
+  "globals": {
+    "person": true
+  }
+}
+```
+
+Variables can be declared in many ways. For variables declared with `class`,
+`const`, or `let`, it is an error to use the variable before/above its
+declaration:
+
+    let firstName = person.firstName;
+    if (firstName === "") {
+      firstName = lastName;
+    }
+    let lastName = person.lastName;
+
+    function printAdjacentPairs(items) {
+      let first = true;
+      for (let current of items) {
+        if (!first) {
+          console.log(previous, current);
+        }
+        let previous = current;
+        first = false;
+      }
+    }
+
+To fix this error, move the variable's declaration up above its use:
+
+    let firstName = person.firstName;
+    let lastName = person.lastName;
+    if (firstName === "") {
+      firstName = lastName;
+    }
+
+Alternatively, declare the variable in an outer scope:
+
+    function printAdjacentPairs(items) {
+      let first = true;
+      let previous;
+      for (let current of items) {
+        if (!first) {
+          console.log(previous, current);
+        }
+        previous = current;
+        first = false;
+      }
+    }

docs/errors/E059.md

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+# E059: assignment to undeclared variable
+
+```config-for-examples
+{
+  "globals": {
+    "isHappy": true
+  }
+}
+```
+
+It is an error to assign to a variable without declaring it:
+
+    tau = Math.pi * 2;
+
+    let emotion;
+    if (isHappy) {
+      emotion = "happy";
+    } else {
+      emotio = "sad";
+    }
+    console.log("I am " + emotion);
+
+To fix this error, declare the variable using `const` or `let`:
+
+    let emotion;
+    if (isHappy) {
+      emotion = "happy";
+    } else {
+      emotion = "sad";
+    }
+    console.log("I am " + emotion);
+
+Alternatively, if the variable is global in your environment, [write a
+quick-lint-js.config file](https://quick-lint-js.com/config/).