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index f755d76..0cdbbd9 100644
--- a/ethereum/source/book/smart-contract/ch04/package-lock.json
+++ b/ethereum/source/book/smart-contract/ch04/package-lock.json
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-			"integrity": "sha1-W2aPT3cTBN/u0XkGRwg4b6ZxeFM=",
+		"socket.io-parser": {
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+			"resolved": "http://registry.npmjs.org/socket.io-parser/-/socket.io-parser-3.4.1.tgz",
+			"integrity": "sha512-11hMgzL+WCLWf1uFtHSNvliI++tcRUWdoeYuwIl+Axvwy9z2gQM+7nJyN3STj1tLj5JyIUH8/gpDGxzAlDdi0A==",
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@@ -602,31 +550,20 @@
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-					"integrity": "sha1-QMRT5n5uE8kB3ewxeviYbNqe/4w=",
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+					"resolved": "http://registry.npmjs.org/debug/-/debug-4.1.1.tgz",
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 					"requires": {
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-					"resolved": "http://registry.npmjs.org/ms/-/ms-0.7.2.tgz",
-					"integrity": "sha1-riXPJRKziFodldfwN4aNhDESR2U="
+					"version": "2.1.3",
+					"resolved": "http://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
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@@ -646,11 +583,6 @@
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@@ -683,18 +615,9 @@
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-			"integrity": "sha1-OS2LotDxw00e4tYw8V0O+2jhBIo="
+			"version": "7.4.2",
+			"resolved": "http://registry.npmjs.org/ws/-/ws-7.4.2.tgz",
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@@ -702,9 +625,9 @@
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-			"integrity": "sha1-GFqIjATspGw+QHDZn3tJ3jUomS0="
+			"version": "1.5.5",
+			"resolved": "https://registry.npmjs.org/xmlhttprequest-ssl/-/xmlhttprequest-ssl-1.5.5.tgz",
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diff --git a/ethereum/source/book/smart-contract/ch04/package.json b/ethereum/source/book/smart-contract/ch04/package.json
index b37c37e..e77f18c 100644
--- a/ethereum/source/book/smart-contract/ch04/package.json
+++ b/ethereum/source/book/smart-contract/ch04/package.json
@@ -3,6 +3,6 @@
 	"dependencies": {
 		"express": "4.14.0",
 		"web3": "0.16.0",
-		"socket.io": "1.6.0"
+		"socket.io": "2.4.0"
 	}
 }