2d:null 2e:["$","title",null,{"children":"Troubleshooting .reverse() | Ryan Cooper | Observable"}] 33:[] 31:{"id":"7116c3ee8e014a4f","slug":"troubleshooting-reverse","title":"Troubleshooting .reverse()","thumbnail":"fec7a095fee39949e7050f877e0c4fa89995c0e34ef98db2c5d6e167301cd67e","access_level":"public","create_time":"$D2019-07-02T12:43:25.966Z","update_time":"$D2019-07-02T13:12:30.721Z","view_time":null,"first_public_time":"$D2019-07-02T13:12:55.885Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"9d55030af7c597b4","login":"maptastik","name":"Ryan Cooper","avatar_url":"https://avatars-next.observableusercontent.com/868e065c57a1f44e8422aaae8c978ef82dc1ada2d596eae26d808adebb8b4b6a","tier":"starter_2024"},"version":55,"publish_version":55,"role":null,"authored":false,"authors":[{"type":"individual","id":"cae231bf35ff5917","login":"maptastik","name":"Ryan Cooper","avatar_url":"https://avatars-next.observableusercontent.com/868e065c57a1f44e8422aaae8c978ef82dc1ada2d596eae26d808adebb8b4b6a","tier":null}],"members":[{"type":"individual","id":"cae231bf35ff5917","login":"maptastik","name":"Ryan Cooper","avatar_url":"https://avatars-next.observableusercontent.com/868e065c57a1f44e8422aaae8c978ef82dc1ada2d596eae26d808adebb8b4b6a","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":0,"collection":null,"type":"notebook","body":{"title":"Troubleshooting .reverse()","cells":[{"id":0,"value":"md`# Troubleshooting .reverse()\nI was working on adding a marker from some GeoJSON data to a Leaflet map and needed to reverse the coordinates of the feature because of the well-documented difference in coordinate order for GeoJSON vs Leaflet. I thought I could just use JavaScript's reverse() method, but ran into some unexpected results. Whenever I ran that method on the coordinate array for the point, it seemed to change the actual GeoJSON rather than return a reversed representation of the coordinate array. This notebook is meant to replicate.\n\n**STOP THE PRESSES**\n\nTurns out, reverse() is an in-place method, meaning it does change the array you apply the method to. D'oh! There's a lesson here: [Read the docs](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse).\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":25,"value":"md`## No reverse\nFirst, let's look at what we get from a coordinate array that is the coordinates value of a GeoJSON feature geometry without running .reverse() on that array.\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":4,"value":"noReverseJson = (await fetch(\"https://services.arcgis.com/v400IkDOw1ad7Yad/arcgis/rest/services/Park_Access_Points/FeatureServer/0/query?where=AP_CODE%3D%27156-004%27&outFields=PARK_NAME&returnGeometry=true&outSR=4326&f=geojson\")).json()","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":20,"value":"noReverseJson.features[0].geometry.coordinates","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"md`Unsurprsingly, the coordinates value array is returned with longitude (X) in the first position and latitude (Y) in the second.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":32,"value":"md`## Reverse coordinates\nNow let's load the same GeoJSON but then reverse values in the coordinates array.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":6,"value":"reverseJson = (await fetch(\"https://services.arcgis.com/v400IkDOw1ad7Yad/arcgis/rest/services/Park_Access_Points/FeatureServer/0/query?where=AP_CODE%3D%27156-004%27&outFields=PARK_NAME&returnGeometry=true&outSR=4326&f=geojson\")).json()","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":7,"value":"reverseJson.features[0].geometry.coordinates.reverse()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":39,"value":"md`OK, so that produced an array with the coordinates reversed. But go back to the cell where we loaded reverseJson and expan the result to show the coordinates value. The coordinates are reversed in the GeoJSON feature as well!\n\n_Note: You may need to re-run the reverseJson cell to produce the observed result_`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W33","stdlib":"1","titling":"auto"}} 32:"$31:body"