joeytwiddle · June 12, 2025 11:44 · Jun 12, 2025 · May 29, 2025 · May 27, 2025 · Apr 30, 2025
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -6,7 +6,7 @@ Fastify logging works differently from `console.log()`. It has a few gotchas.
 
 - If you want to **log an error**, it must be the first argument, and _not_ a property inside an object. You may add your own string message as the second argument (optional but recommended).
 - If you want to **log an object**, then put the object as the first argument, and again an optional message string as the second argument.
-- But beware: If the "object" you are logging is **actually a string**, then _do not_ put it as the first variable, concatenate it instead.
+- But beware: If the "object" you are logging is **actually a string**, then _do not_ put it as the first variable. Either wrap it inside an object, or concatenate it into your message.
 
 ## Patterns which **WORK**
 

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -39,6 +39,9 @@ fastify.log.info(stringVariable, "message")
 // An error deep inside an object does not get serialized properly.
 // This will only log: msg: "test_log", error: {}
 fastify.log.info({ error }, "message")
+// Unfortunately this means we cannot log both an error and some contextual data at the same time
+// My solution to this is to send two logs, one with data, and one with the error
+// Please correct me if there is a better way!
 ```
 
 ## And one more surprising case:

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -4,8 +4,8 @@ Fastify logging works differently from `console.log()`. It has a few gotchas.
 
 ## TLDR
 
-- If you want to **log an object**, then put the object as the first argument, and (optionally) a message string as the second argument.
-- If you want to **log an error object**, it must be the first argument, and not a property inside an object.
+- If you want to **log an error**, it must be the first argument, and _not_ a property inside an object. You may add your own string message as the second argument (optional but recommended).
+- If you want to **log an object**, then put the object as the first argument, and again an optional message string as the second argument.
 - But beware: If the "object" you are logging is **actually a string**, then _do not_ put it as the first variable, concatenate it instead.
 
 ## Patterns which **WORK**
@@ -25,19 +25,19 @@ fastify.log.debug({ foo: 'bar' }, { baz: 'qux' })
 // Through pino, this will appear as: {baz: "qux"}, foo: "bar"
 ```
 
-## Patterns which unexpectedly **DO NOT WORK**
+## Patterns which surprisingly **DO NOT WORK**
 
 ```javascript
 // Providing a string as the first argument? Only the first argument gets logged!
-// Does not log the data
+// This will not log the data
 fastify.log.info("message", { data })
-// Does not log the variable
+// This will not log the variable
 fastify.log.info("message", stringVariable)
-// Does not log the message
+// This will not log the message
 fastify.log.info(stringVariable, "message")
 
-// An error deep inside an object does not get serialized.
-// Only logs: msg: "test_log", error: {}
+// An error deep inside an object does not get serialized properly.
+// This will only log: msg: "test_log", error: {}
 fastify.log.info({ error }, "message")
 ```
 

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -39,9 +39,13 @@ fastify.log.info(stringVariable, "message")
 // An error deep inside an object does not get serialized.
 // Only logs: msg: "test_log", error: {}
 fastify.log.info({ error }, "message")
+```
+
+## And one more surprising case:
 
-// Logging a msg property does not appear, but logging a message property does!
-// I'm not sure if this is always true for Fastify. It might just be in my current project.
+```javascript
+// When logging a string property, it does not appear if I use the key 'msg', but it does with key 'message'
+// I'm not sure if this is always true for Fastify.  It might just be in my current project.
 fastify.log.info({ val, msg }, "only val will be logged")
 fastify.log.info({ val, message }, "both val and message will be logged")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -39,4 +39,9 @@ fastify.log.info(stringVariable, "message")
 // An error deep inside an object does not get serialized.
 // Only logs: msg: "test_log", error: {}
 fastify.log.info({ error }, "message")
+
+// Logging a msg property does not appear, but logging a message property does!
+// I'm not sure if this is always true for Fastify. It might just be in my current project.
+fastify.log.info({ val, msg }, "only val will be logged")
+fastify.log.info({ val, message }, "both val and message will be logged")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -1,10 +1,15 @@
-TLDR:
-- If you want to log an object, put the object as the first argument, and (optionally) a message string as the second argument.
-- If you want to log an error object, it must be the first argument, and not a property inside an object.
-- (As a result, I don't know how to log an error and also an object for context, but it might be possible.)
-- But beware: If the "object" you are logging is actually a string, then _do not_ put it as the first variable, concatenate it instead.
+# Logging in Fastify
+
+Fastify logging works differently from `console.log()`. It has a few gotchas.
+
+## TLDR
+
+- If you want to **log an object**, then put the object as the first argument, and (optionally) a message string as the second argument.
+- If you want to **log an error object**, it must be the first argument, and not a property inside an object.
+- But beware: If the "object" you are logging is **actually a string**, then _do not_ put it as the first variable, concatenate it instead.
+
+## Patterns which **WORK**
 
-Patterns which are **WORKING**:
 ```javascript
 // Logging one string
 fastify.log.info("message")
@@ -16,11 +21,12 @@ fastify.log.info(error, "message")
 fastify.log.info({ data, foo, bar, baz }, "message")
 
 // You can also log two objects, although the second will be treated as the msg
-// This logs: msg: {baz: "qux"}, foo: "bar"
 fastify.log.debug({ foo: 'bar' }, { baz: 'qux' })
+// Through pino, this will appear as: {baz: "qux"}, foo: "bar"
 ```
 
-Patterns which unexpectedly **DO NOT WORK**:
+## Patterns which unexpectedly **DO NOT WORK**
+
 ```javascript
 // Providing a string as the first argument? Only the first argument gets logged!
 // Does not log the data

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -6,12 +6,18 @@ TLDR:
 
 Patterns which are **WORKING**:
 ```javascript
+// Logging one string
 fastify.log.info("message")
 fastify.log.info("message: " + stringVariable)
 fastify.log.info(`message: ${stringVariable}`)
 
+// Puttting the error or context object first, and the log message second
 fastify.log.info(error, "message")
 fastify.log.info({ data, foo, bar, baz }, "message")
+
+// You can also log two objects, although the second will be treated as the msg
+// This logs: msg: {baz: "qux"}, foo: "bar"
+fastify.log.debug({ foo: 'bar' }, { baz: 'qux' })
 ```
 
 Patterns which unexpectedly **DO NOT WORK**:
@@ -25,6 +31,6 @@ fastify.log.info("message", stringVariable)
 fastify.log.info(stringVariable, "message")
 
 // An error deep inside an object does not get serialized.
-// Only logs: "msg": "test_log", "error": {}
+// Only logs: msg: "test_log", error: {}
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -24,7 +24,7 @@ fastify.log.info("message", stringVariable)
 // Does not log the message
 fastify.log.info(stringVariable, "message")
 
-// An error deep inside an object does not get serialised.
+// An error deep inside an object does not get serialized.
 // Only logs: "msg": "test_log", "error": {}
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -11,7 +11,7 @@ fastify.log.info("message: " + stringVariable)
 fastify.log.info(`message: ${stringVariable}`)
 
 fastify.log.info(error, "message")
-fastify.log.info({ data }, "message")
+fastify.log.info({ data, foo, bar, baz }, "message")
 ```
 
 Patterns which unexpectedly **DO NOT WORK**:

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -14,16 +14,17 @@ fastify.log.info(error, "message")
 fastify.log.info({ data }, "message")
 ```
 
-Patterns which **DO NOT WORK**:
+Patterns which unexpectedly **DO NOT WORK**:
 ```javascript
-// String as the first argument? Only the first argument gets logged!
-// Only logs the message, ignores the data object!
+// Providing a string as the first argument? Only the first argument gets logged!
+// Does not log the data
 fastify.log.info("message", { data })
 // Does not log the variable
 fastify.log.info("message", stringVariable)
 // Does not log the message
 fastify.log.info(stringVariable, "message")
 
-// Error deep inside an object does not get serialised. It only logs: "msg":"test_log","error":{}
+// An error deep inside an object does not get serialised.
+// Only logs: "msg": "test_log", "error": {}
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -16,13 +16,14 @@ fastify.log.info({ data }, "message")
 
 Patterns which **DO NOT WORK**:
 ```javascript
-// Two string arguments? Only the first argument get logged!
+// String as the first argument? Only the first argument gets logged!
+// Only logs the message, ignores the data object!
+fastify.log.info("message", { data })
+// Does not log the variable
 fastify.log.info("message", stringVariable)
+// Does not log the message
 fastify.log.info(stringVariable, "message")
 
-// Object as the second argument? Only logs the message, ignores the data object!
-fastify.log.info("message", { data })
-
 // Error deep inside an object does not get serialised. It only logs: "msg":"test_log","error":{}
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -23,6 +23,6 @@ fastify.log.info(stringVariable, "message")
 // Object as the second argument? Only logs the message, ignores the data object!
 fastify.log.info("message", { data })
 
-// Error deep inside an object? Only logs: message { error: {} }
+// Error deep inside an object does not get serialised. It only logs: "msg":"test_log","error":{}
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -23,6 +23,6 @@ fastify.log.info(stringVariable, "message")
 // Object as the second argument? Only logs the message, ignores the data object!
 fastify.log.info("message", { data })
 
-// Error deep inside an object? Only logs: { error: "[object Error]" }
+// Error deep inside an object? Only logs: message { error: {} }
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -16,13 +16,13 @@ fastify.log.info({ data }, "message")
 
 Patterns which **DO NOT WORK**:
 ```javascript
-// Only the first arguments get logged!
+// Two string arguments? Only the first argument get logged!
 fastify.log.info("message", stringVariable)
 fastify.log.info(stringVariable, "message")
 
-// Only logs the message, ignores the data object!
+// Object as the second argument? Only logs the message, ignores the data object!
 fastify.log.info("message", { data })
 
-// Only logs: { error: "[object Error]" }
+// Error deep inside an object? Only logs: { error: "[object Error]" }
 fastify.log.info({ error }, "message")
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -2,16 +2,24 @@ TLDR:
 - If you want to log an object, put the object as the first argument, and (optionally) a message string as the second argument.
 - If you want to log an error object, it must be the first argument, and not a property inside an object.
 - (As a result, I don't know how to log an error and also an object for context, but it might be possible.)
+- But beware: If the "object" you are logging is actually a string, then _do not_ put it as the first variable, concatenate it instead.
 
 Patterns which are **WORKING**:
 ```javascript
 fastify.log.info("message")
+fastify.log.info("message: " + stringVariable)
+fastify.log.info(`message: ${stringVariable}`)
+
 fastify.log.info(error, "message")
 fastify.log.info({ data }, "message")
 ```
 
 Patterns which **DO NOT WORK**:
 ```javascript
+// Only the first arguments get logged!
+fastify.log.info("message", stringVariable)
+fastify.log.info(stringVariable, "message")
+
 // Only logs the message, ignores the data object!
 fastify.log.info("message", { data })
 

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -3,14 +3,14 @@ TLDR:
 - If you want to log an error object, it must be the first argument, and not a property inside an object.
 - (As a result, I don't know how to log an error and also an object for context, but it might be possible.)
 
-Working patterns:
+Patterns which are **WORKING**:
 ```javascript
 fastify.log.info("message")
 fastify.log.info(error, "message")
 fastify.log.info({ data }, "message")
 ```
 
-Patterns which don't work:
+Patterns which **DO NOT WORK**:
 ```javascript
 // Only logs the message, ignores the data object!
 fastify.log.info("message", { data })

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -1,7 +1,7 @@
 TLDR:
 - If you want to log an object, put the object as the first argument, and (optionally) a message string as the second argument.
-- If you want to log an error, it must be the first argument, and not deep inside an object.
-- (I don't know how to log an error and also an object for context, but it might be possible)
+- If you want to log an error object, it must be the first argument, and not a property inside an object.
+- (As a result, I don't know how to log an error and also an object for context, but it might be possible.)
 
 Working patterns:
 ```javascript

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -1,5 +1,5 @@
 TLDR:
-- If you want to log an object, put the object as the first argument, and (optionally) the message string as the second argument!
+- If you want to log an object, put the object as the first argument, and (optionally) a message string as the second argument.
 - If you want to log an error, it must be the first argument, and not deep inside an object.
 - (I don't know how to log an error and also an object for context, but it might be possible)
 

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -12,9 +12,9 @@ fastify.log.info({ data }, "message")
 
 Patterns which don't work:
 ```javascript
+// Only logs the message, ignores the data object!
+fastify.log.info("message", { data })
+
 // Only logs: { error: "[object Error]" }
 fastify.log.info({ error }, "message")
-
-// Only logs the message!
-fastify.log.info("message", { data })
 ```
diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -1,5 +1,5 @@
 TLDR:
-- If you want to log an object, put the object as the first argument, and the message string as the second argument!
+- If you want to log an object, put the object as the first argument, and (optionally) the message string as the second argument!
 - If you want to log an error, it must be the first argument, and not deep inside an object.
 - (I don't know how to log an error and also an object for context, but it might be possible)
 

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -12,7 +12,7 @@ fastify.log.info({ data }, "message")
 
 Patterns which don't work:
 ```javascript
-// Only logs: `error: "[object Error]"`
+// Only logs: { error: "[object Error]" }
 fastify.log.info({ error }, "message")
 
 // Only logs the message!

diff --git a/logging_in_fastify.md b/logging_in_fastify.md
@@ -4,14 +4,14 @@ TLDR:
 - (I don't know how to log an error and also an object for context, but it might be possible)
 
 Working patterns:
-```
+```javascript
 fastify.log.info("message")
 fastify.log.info(error, "message")
 fastify.log.info({ data }, "message")
 ```
 
 Patterns which don't work:
-```
+```javascript
 // Only logs: `error: "[object Error]"`
 fastify.log.info({ error }, "message")
 

diff --git a/gistfile1.txt → logging_in_fastify.md b/gistfile1.txt → logging_in_fastify.md
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,20 @@
+TLDR:
+- If you want to log an object, put the object as the first argument, and the message string as the second argument!
+- If you want to log an error, it must be the first argument, and not deep inside an object.
+- (I don't know how to log an error and also an object for context, but it might be possible)
+
+Working patterns:
+```
+fastify.log.info("message")
+fastify.log.info(error, "message")
+fastify.log.info({ data }, "message")
+```
+
+Patterns which don't work:
+```
+// Only logs: `error: "[object Error]"`
+fastify.log.info({ error }, "message")
+
+// Only logs the message!
+fastify.log.info("message", { data })
+```
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