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104 lines
3.0 KiB
104 lines
3.0 KiB
Using the JavaScript VM
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========================
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There are 3 type of environments Remix can be plugged to:
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`Javascript VM`, `Injected provider`, or `Web3 provider`. (for details see [Running transactions](http://remix.readthedocs.io/en/latest/run_tab.html))
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Both `Web3 provider` and `Injected provider` require the use of an
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external tool.
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The external tool for `Web3 provider` is an Ethereum node the tools for
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`Injected provider` are Mist or Metamask.
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The `JavaScript VM` mode is convenient because each execution runs in
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your browser. Thus reloading the page will restart Remix with an empty
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state.
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So for performance purposes, it might also be better to use an external
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node.
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Selecting the VM mode
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---------------------
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Make sure the VM mode is selected. All accounts displayed in `Accounts`
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should have 100 ether.
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Sample contract
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---------------
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``` {.sourceCode .none}
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pragma solidity ^0.4.16;
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contract testContract {
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uint value;
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function testContract(uint _p) {
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value = _p;
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}
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function setP(uint _n) payable {
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value = _n;
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}
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function setNP(uint _n) {
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value = _n;
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}
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function get () constant returns (uint) {
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return value;
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}
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}
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```
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This contract is very basic. The goal is to quickly start to create and
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to interact with a sample contract.
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Deploying an instance
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---------------------
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The `Compile tab` displays information related to the current contract
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(note that there can be more than one) (see ../compile\_tab).
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Moving on, in the `Run tab` select, `JavaScript VM` to specify that you
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are going to deploy an instance of the contract in the `JavaScript VM`
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state.
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The constructor of `testContract` needs a parameter (of type `uint`).
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Give any value and click on `Create`.
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The transaction which deploys the instance of `testContract` is created.
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In a "normal" blockchain, it can take several seconds to execute. This
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is the time for the transaction to be mined. However, because we are
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using the `JavaScript VM`, our execution is immediate.
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The terminal will inform you about the transaction. You can see details
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there and start debugging.
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The newly created instance is displayed in the `run tab`.
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Interacting with an instance
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----------------------------
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This new instance contains 3 actions which corresponds to the 3
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functions (`setP`, `setPN`, `get`). Clicking on `SetP` or `SetPN` will
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create a new transaction.
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Note that `SetP` is `payable` (red action) : it is possible to send
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value (Ether) to the contract.
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`SetPN` is not payable (light red action) : it is not possible to send
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value (Ether) to the contract.
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Clicking on `get` will not execute a transaction (blue action). It is
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not necessary to do so because `get` does not modify the state (variable
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`value`) of this instance.
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As `get` is `constant` you can see the return value just below the
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action.
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